The Start Living in 2012 inaugural meetup.

Around 8 p.m. on a recent Monday, about 35 people of disparate ages were sitting on the marble steps of the public atrium inside Two World Financial Center, listening to a 25-year-old in baggy jeans named Jordan Phoenix talk about Living. “This is the class where we figure out who we are and what we want to do with our lives,” he told his audience, a range of artists and professionals, employed and unemployed, 20-somethings and middle-aged divorcees who, like me, were drawn in by Mr. Phoenix’s aggressive pitch on the website Meetup.com.

As the post had put it: “This group is for you if you know you are capable of greatness, but are unclear and frustrated about how to get there.” The group, “Start Living in 2012,” had picked up more than 100 members in three days, which made it a very fast-growing meetup group indeed.

“I love that everyone here showed up,” Mr. Phoenix said. “Sixty-eight people RSVP’ed. Thirty people didn’t show up. Guess what? They’re not invited to the next meetup, because they’re bullshit artists.”

I had no intention of going to the next meetup. As much as I want to start living in 2012, I was merely a tourist.

Meetup is a website where strangers with common interests can organize get-togethers. In New York, where it started, it has become a compendium of microsubcultures. I have a small habit of peeking at Meetup every once in a while, just reading the descriptions and marveling at how nudists, Dungeons & Dragons players and “male cat lovers” talk when they’re speaking just to one another. (“We celebrate and cherish our cats. We are male. Sometimes we feel like no one understands us when you show them pictures of your cat or share stories about its adventures in your apartment.") There are meetups for Satanists and ukulele players, swingers and “deep thinkers,” as well as a wealth of groups for people “just doing their daily shit,” as one Meetup employee put it. Voyeuristically, it’s richer than Craigslist’s missed connections and more authentic than New York’s sex diaries.

Meetup is a strange world for the average ironical urbanite. For me, socializing revolves around drinking, primarily with people I already know. And as much as I grouse about both of those facts, I had the same feelings about Meetup that I did about online dating: it’s something other people do.

My attitude was common, Scott Heiferman, the co-founder and CEO of Meetup, told me in a recent phone interview. “Anyone can look at Meetup and say ‘Oh, that’s really wonderful,’” he said. “And you say ‘what about you?’ And they say, ‘Well, that’s not for me. I’m not that kind of person. I don’t have those kinds of needs.’” Mr. Heiferman, of course, believes Meetup is for everyone. Recently, a misanthropic photographer dismissed Meetup as being “not for him.” “I don’t really like people,” he told Mr. Heiferman. But after joining a professional meetup group to trade leads, share vendors and collaborate on projects, the photographer admitted he’d been wrong. It was great for business, he said, and the people were great too.

“When people hear about Meetup for the first time and it's outside the context of a tech meetup or moms meetup, they think it must be some dating thing,” Mr. Heiferman said. “Because why the hell would you want to meet people, if not to hook up or get money? Like, why on earth would you want to talk to anybody that you don't already know, if not for sex or money?”

But about six months ago, my curiosity spilled over into the real world. I was scouring the site for a book club for my overworked mom; instead I came across the NYC Freegan Meetup, which was hosting a dumpster diving tour in my neighborhood that evening. My motivation was mostly anthropological. I didn’t mind taking home a few scavenged bagels, but really I wanted to meet these freegans and study their ways. But as my fellow dumpster divers and I delighted over an intact box of Godiva chocolate bars and passed around sleeves of perfectly good saltines, I found myself wondering, could Meetup work for me?

On Tuesday around 8 p.m., a companion and I walked into West 3rd Common, a low-lit bar with red banquettes where about eight people were playing cards on low cherrywood tables. This was the East Village Euchre Club.
The card players, all in their 20s and 30s, included students, a pair of engineers, a Rochester native who was also a member of the Brooklyn Euchre Club, and a long-haired martinet named James, who had brought the cards and made sure conversations didn’t distract players from the hand.

Meetups need at least four attendees to be a good experience, according to Meetup, the company. The norm is for a meetup to start really, really small, with one or two people, and either grow slowly or die out. Occasionally meetups will catch fire, like Start Living in 2012, and attract a bunch of members all at once.

The East Village Euchre Club had 15 people at its first game in September, and has hosted more than a game a week since then, enough to qualify it as a a SMUG, or Successful Meetup Group, in Meetup parlance.
Most of the talk was of euchre, a trump game popular in the Midwest, interspersed with rote introductions. What do you do? When did you move to New York? Three hours later, and we still knew very little about each other, but it was after midnight and the four players at my table were the last patrons in the bar.

Mr. Heiferman started Meetup as a lonely midwestern transplant himself. Quiet, political, and smart, he moved to New York in part to be near his favorite band, Luna, a punk collective with a cult following. “My entire experience of going out to see this band was, I would grab a bite to eat by myself and I would go to the show, and I’d stand there, and I wouldn’t talk to anybody,” he said. “Then I’d filter out, staring at my shoes. Maybe it’s just being shy, or I don’t know what, but there was no context for being allowed to talk to anyone.”

Then in September of 2001, everyone in New York suddenly had permission to talk to each other. The introverted Mr. Heiferman found himself having conversations with his neighbors, and he liked it. A few weeks later, he bought a copy of "Bowling Alone," a chronicle of the disappearance of bowling leagues, church groups and other social clubs, and the accompanying effect on our health and democracy. Every new employee at Meetup is given a copy of "Bowling Alone." In the book, the author cites the Internet as one of the causes of rifts between Americans. Mr. Heiferman and a friend, Matt Meeker, thought the Internet could be a solution.

Even if it hasn’t fully reconstructed the tradition of community in America, 11 years later Meetup is at least a window into hidden corners of the city. It’s also a directory of the best public meeting spaces. The bustling Citicorp Atrium on Lexington and 53rd, which has free wifi, is a favorite. Every white table was occupied with couples, students or homeless men munching sandwiches, as I made my way toward a meetup in the corner on a recent Wednesday evening.

An older gentleman in a Coney Island sweatshirt, possibly in his 60s or 70s, was seated at a table with a plump blonde woman, Brenna, and her soft-spoken co-organizer, David. I introduced myself and scooted over a metal chair as David passed out a detailed worksheet. “NYC Hoarders-No-More Meetup Group,” it said. We were joined by a tattooed hoarder from the Bronx who sleeps in his living room because his bedroom is stuffed to the ceiling with junk, books, and defunct scuba gear. “I’m an atheist,” he said. “But I pray for a fire.”

A few more hoarders showed up as we worked our way through everyone’s updates. Brenna had thrown away about ten New Yorkers, some greeting cards and a notebook with amateur song lyrics that she had found on the sidewalk; Adrian, a former bank vice president, had made significant progress in the kitchen (“The freezer part is cool but the refrigerator part is out of control”).

Every week, the hoarders bring in some debris to discard. As they sorted, we talked about Meetup.

“I think there should be a values score on Meetup so you can put in your values and find meetups based on that,” said a grandfather-aged gentleman with wispy ear hair and rubber bands around his wrist.

“I love Meetup—I’m in a bunch of them,” said the Bronx hoarder. “I co-organize the New York City Depression Meetup. It has 900-some members.”

He joined the site for a scuba diving meetup and was on it for a year before he realized the site had other relevant offerings; now, he regularly checks the site whenever he develops a new interest. “I joined an evolution meetup and the book we read was Richard Dawkins, "The Greatest Show on Earth," and I fell in love with it,” he said. “After that, I started going to atheism meetups.”

David, who is a member of 15 meetup groups, asked him to write down the name of the depression meetup.

Meetup tends to be addicting. “I am very active on Meetup, in that I join a lot of Meetup groups to see what people are doing,” one Start Living in 2012 attendee wrote in an email. “Meetup probably e-mails me an average of five new groups a day for me to look at, and of those I may sign on to receive updates from one or two a week. Off the top of my head, I've been to meetings of a Beekeeping meetup, a Content Strategy meetup, an Artists Accountability Group meetup, and an Online Dating Conference meetup.”

It’s interesting to see what will motivate people to meet up. The site first got traction when the founders started inventing holidays. Mr. Heiferman and Mr. Meeker scoured the Internet for groups and special interest blogs. Then they sent the groups an email about an upcoming made-up celebration—International Pug Lovers Meetup Day, for example—and explained how to join a local meetup or host one. Today, there are 39,427 members of 179 Pug Meetup groups in 149 cities around the world. The biggest demographic on Meetup is moms. Political groups are also big, as are singles groups and New Age-y interests like “energy healing.” Group activities like language practice, sports and networking events are popular. There are even a few pickup artist-themed meetups, like the NYC Wingmen.

On a recent Friday night, I ventured out to an electronic rock show on the Lower East Side for a meetup of NYC Bands for Bands, a sort of networking group of musicians who go to each others’ shows. One musical couple started the group five months ago in order to meet promoters’ demands that their band bring a crowd. But filling up the club is part of it, Micha, a musician in a plaid cap, told me; he comes for the camaraderie. “I can’t imagine myself not going to this for as long as it exists,” he said.

With the glaring exception of the New York Tech Meetup, which has more than 20,000 members, meetups seem to have a natural size limit. Once a group gets large enough, it starts to replicate or “cell divide” according to set patterns, Mr. Heiferman said. “It’s an almost Darwininan ecosystem,” he said. Lance, a stay-at-home father, started the NYC Dads Meetup in 2008 as a group for at-home dads, but it’s expanded. “We’ve got dads of all stripes,” the group’s co-organizer Lance, told me at a NYC Dads drink-up at Heartland Brewery in Union Square. “Guys who lost their jobs, guys who chose the role. We’ve got gay dads joining now.”

The group now has a popular blog, a long list of sponsors, and business cards. But Mr. Heiferman, who is a member of NYC Dads, decided neither it nor any of the other 50 parenting meetups on the Upper West Side was quite right, so he recently started a splinter meetup for parents of children on the aged 9 to 16 months. It now has 29 members.

I felt I had just scratched the surface, even after a week of random meetups. I didn’t get all my first choices. Organizers of the NYC Vinyl Meetup did not email me back quickly enough; I picked the hoarders group over the A Course In Miracles Meetup Group, devotees of the cult classic spiritual text. I got a few rejections. “The 3 p.m. sword balancing is for folks that have 2-3 years of belly dance experience,” wrote the organizer of the Manhattan Tribal ATS Tribal Belly Dance Meetup NYC, somewhat of a relief. I was also excluded from a private dinner held by the Psychedelic and Entheogenic Society, fans of Timothy Leary, although most of their meetups are open.

There was a spate of meetups on Saturday morning—running, walking, breakfast clubs—that I slept too late to check out, opting for Exciting NYC Mandarin Chinese Learners at 2 p.m. at the Chinatown Y. The class was $40. This is not unusual; independent teachers use Meetup to coordinate and advertise classes, and some business-oriented events also charge a fee. Meetup has made this easier by integrating PayPal. Every meetup group organizer pays $10 a month.

For the final outing in my week-long experiment, I caught a nighttime gathering of the New York Parkour Meetup. I was soon in pain from banging my body as I tried to hurdle over stacks of mats while our limber instructor heckled at us to do flips. Luckily, this session took place inside the colorful gymnasium in the Field House at Chelsea Piers, and not at the Sanctuary, the group’s concrete Upper West Side practice area.

I walked out into the icy night exhausted—partly because of the exertion, partly because I had just spent the last week hanging out with strangers. In that moment, I thought, if I never, ever saw another human, it would be too soon. At least until Tuesday. That was Euchre night.

CORRECTION: An earlier version of this story incorrectly identified a New York punk band as Lunar; the band is Luna. Betabeat regrets the error.