Benjamin Ling, the senior Facebook executive who joined the social network barely a year ago from Google, is heading back to the mothership to figure out how to make money off online video-sharing Web site YouTube, All Things Digital reports.

Facebook confirmed Ling’s departure, saying that he’s leaving to pursue other interests. “We wish him well and appreciate his great contributions to the early success of Facebook Platform.” Ling didn’t return a call (but you can contact him here), and a YouTube spokeswoman declined to comment on rumors or speculation.

When Ling quit Google last year to join Facebook, blogs buzzed with how the move heralded a trend of Google employees joining Silicon Valley’s hottest company. Although that did happen somewhat — Sheryl Sandberg and Elliot Schrage being two ex-Googlers who are now top executives at Facebook — the social network has been losing people too.

Two months ago, Matt Cohler, vice president of product management, left to join Benchmark Capital, a venture capital firm. Here’s a list of some other recent Facebook departures. 

As for Ling,who led Facebook’s recent redesign efforts as director of platform product management, he’s got his work cut out for him at YouTube.

The Wall Street Journal reported in July that ad revenue from YouTube this year was likely to fall short of parent Google’s expectations. Google’s CEO Eric Schmidt has acknowledged they’re not quite sure how to make money off the millions of visitors to the popular online video-sharing site.

“We don’t yet know how we are going to make significant amounts of money on YouTube,” Schmidt said in an on-stage interview with The New Yorker’s Ken Auletta. “But it seems obvious we should be able to make some money from this,” adding that Google is moving to transform YouTube into a money-maker via new forms of advertising it plans to unveil in the coming year.

Picture: Ben Ling with Facebook CEO Mark Zuckerberg (Reuters)