Wehner. (Photo: Zynga.)

David Wehner is out at Zynga and David Ko is up, as the social gaming company shook up its C-suite in an announcement after stock markets closed.

Mr. Wehner, who's served as the company's chief financial officer since coming over from investment bank Allen & Co. in 2010, may have lost Wall Street's confidence after Zynga's share price plummeted nearly 80 percent since the FarmVille maker's IPO at $10 last December.

He's not the first high-level employee to leave Zynga in recent months, nor have the departures been limited to the top executives: Zynga laid off about 150 employees last month, and it said it would shut down 13 games.

While Mr. Wehner moves on to a senior finance job at Facebook, he'll be replaced by Mark Vranesh, who returns to the CFO role he filled from 2008 to 2010, following a two-year stint as Zynga's chief accounting officer.

Meanwhile, Zynga took the opportunity to reward Mr. Ko, regarded as a rising star within the company for his work heading its mobile efforts, promoting the former Yahoo employee to chief operating officer. In addition to Mr. Ko's work with mobile, he's been charged with supervising Zynga offerings such as With Friends, Casino and Draw Something.

"Dave remains a good friend to us all and we wish him success in his next role," Zynga founder and CEO Mark Pincus said in a release. "I'm confident we have the right team to deliver on our mission of connecting the world through games and position us for long-term growth."