Mr. Zhou.

Wondering what happened to Turntable.fm's fast following, Xoogler-founded cousin, Rolling.fm? The social music site has been serving up errors for about two weeks; Tenka, the founders' previous startup, is also gone. Co-founder and chief product officer Tim Zhou, whose resume includes IBM and Google, did not respond to a request for comment by email, and now we know why.

It looks like Tumblr recently nabbed itself an Xoogler. Mr. Zhou created a Tumblr about one month ago and is now listed on the startup's staff page alongside 68 other employees (Tumblr, you're getting so big!)

We reached out to Mr. Zhou again this morning for comment. Our speculation? Rolling, a drastic pivot from deals provider Tenka, failed to raise money after being posted on AngelList (perhaps in part because no one wanted to compete against the golden child, Turntable).

Tumblr, meanwhile, is still hiring for eight open engineering positions as well as for Dutch and Swedish speaking ambassadors.

Indeed, Rolling.fm does not resolve and the last tweet was on November 19. Rolling's precursor, a social deals site called Tenka.com, is also not resolving.

The Facebook app had about 200 daily active users a month ago; now it has none, according to AppData. There's evidence that Rolling was active until at least Dec. 15, when the producer duo Dada Life premiered a remix there; Bnet interviewed the startup on Dec. 8.

Tim Zhou, Rolling's chief product officer, did not respond to an email request for comment. At present, the mysterious disappearance of Rolling.fm would appear to be due to three possible reasons:

1. Forgot to renew domain*
2. Cease and desist notice from scary record label
3. Failed to gain enough traction or funding, cofounders gave up on it (even Turntable's traffic has been slipping)

*A reader points out that the domain expires in 2012, so this explanation is unlikely.

Rolling.fm caught some flak from the internet when it launched in the wake of Turntable.fm's extreme success. The founders admitted they duped the idea, but appealed to the internet's tradition of innovation. (Even Steve Jobs subscribed to the doctrine of "good artists copy, great artists steal.")

The cofounders had pivoted from Tenka, a deals site that raised from seed investors including StubHub's Jeff Fluhr, Great Oaks Venture Capital's Ben Lin and Raj Sandhu, formerly of the Soros Fund. The site was available outside the U.S., unlike Turntable, which let them grab some easy users.

The cofounders switched to building Rolling in May, they said, which would mean Rolling had about a seven month run before giving up the ghost. But the co-founders put the startup on AngelList about nine months ago. We'll update as we learn more.

Users felt a sense of deja-vu when Rolling.fm, an interactive music streaming start-up, launched just over a week ago. Rolling.fm's interface--a virtual club with DJs lined up at a laptop and a floating chat room--looks so much like viral hit Turntable.fm that users, along with Betabeat's own numero uno Turntable fanboy, @benpopper, immediately started calling it a knock-off and questioning its legitimacy. (One Betabeat tipster claimed the app, which has 2,400 daily average users according to the most recent numbers from AppData, is populated by fake avatars).

Rolling is hardly the first pop-up app inspired by Turntable.fm's innovation and success. But the app, made by the three ex-Google co-founders of the daily deals / social media advertising start-up Tenka, features all the Turntable calling cards: avatars of DJs and listeners, rotating DJ spots, and a "weak-hot" rating system that can get DJs points or get a song skipped.

After some initial dodginess about where the idea came from, Rolling.fm's founders are ready to own- up to their origins. "I think it's obvious that the initial version of Rolling is inspired by Turntable," co-founder Tim Zhou said in an email. "To say otherwise is not accurate. We started working on our pivot in late May."

Back in early spring, Mr. Zhou and two fellow Xooglers were working on the daily deals / social media advertising start-up Tenka, which is now on standby. They started working on ideas for a graphical interface resembling early adventure games ("You see a cupcake"), at least one of which featured a central element of Turntable. Betabeat took a look at some early mock-ups, but Rolling's counsel has advised them against publishing their records.

So the team was losing steam on Tenka and brainstorming pivots when they saw Turntable.fm. The vision clicked and they had an app up in about half the time it took the trio behind StickyBits to build Turntable.

"We ultimately have different product visions for this thing," Mr. Zhou said. Rolling has already rolled out a nifty new feature--a virtual "restroom" where users can DJ, chat and spraypaint graffiti on the walls.

Other differences between Rolling.fm and Turntable include:

• Turntable.fm is restricted to users in the U.S., while Rolling.fm is still available internationally. That and a targeted marketing effort directed at universities may be why Rolling.fm, despite being buggier and much less slick, has already seen an impressive peak of 8,500 daily users last week, according to AppData, although the site is much quieter today. Turntable has around 21,000 daily average users.
• Where Turntable had a rise of company rooms, the majority of rooms on Rolling.fm are alma mater-specific. And despite hearing criticism that the site appeared populated but was actually dead, Betabeat found some highly-active rooms where conversation was tripping along at the same coked-out speed you see in, say, the Coding Soundtrack room on Turntable.
• DJ points. One frequent criticism of Turntable is that DJs dominate a room and never let anyone else play. But on Rolling, DJs get nicked points when users vote against their tracks--making the DJ rankings a lot more volatile and lowering the barrier to entry for new DJs.
• Little things: Rolling lets users buy virtual goods with DJ credits in the form of little pieces of flair--crowns and bling for your avatar; you can also privately message individual users whereas Turntable is restricted to the room's group chat.
• And features yet to come. "We will be releasing additional room formats like DJ battles soon," Mr. Zhou said.

Start-ups tend to spring up in crowds, as we've seen with the recent spate of group buying and group texting. In the interactive music space, there's Console.fm, based out of the 500Startups incubator in Mountain View and built in three days, which appeals to the anti-social social music streamers who want the freedom to set it and forget it, knowing that whatever playlist they've chosen has been vetted by users on SoundCloud and it's easy to skip if a beat is not to one's liking. There's Outloud.fm, based in New York, which rose up around the same time as Turntable in early April and provides much of Turntable's "everyone's a DJ!" functionality, just without the cute graphics. And the precursor, Listening Room, possibly the Ur-app of this crop of interactive, socially-informed streaming music start-ups.

When asked what Turntable thought of Rolling.fm, co-founder Billy Chasen said, "We are still waiting until we are out of private beta until we talk and give interviews / comments.  Right now we're just focused on scaling our own product and making it better for public beta." May the best app win.