Facebook's Original Biz Dev Chief Leaves

Today ends almost five years of Alison "Ali" Rosenthal leading the Facebook's business development team.

Alison “Ali” Rosenthal is leaving Facebook today, after leading the company’s business bevelopment team for five years.

Although she has no immediate plans for the future, Alison “Ali” Rosenthal’s last day at Facebook is today. She might get involved in another start-up, she told Liz Gannes at NetworkEffect, although the Stanford alumna wouldn’t reveal where she might land.

We wonder whether she already has a startup empoloyer lined up, namely one that is operating in stealth mode, which would preclude her from divulging details to the press. Business development work often involves interaction with startups that make job offers. And it wouldn’t surprise if her next project had a mobile focus.

Since joining Facebook in February 2006, Rosenthal developed some 300 relationships with mobile companies around the world. Her nearly five years at the company focused on expanding the mobile presence of the social network. Out of Facebook’s 250 million users in 2009, 65 million checked the site through a mobile device. That doubled over the following year, when the social network’s software became the most popular app on the iPhone and Blackberry, along with second most popular for Droids.

In the past few months, a number of Facebook’s earliest hires have left to start new projects, often without revealing where they were going when giving notice to the social network. The most recent example was company’s original moneymaking strategist, Tim Kendall, who held the title director of monetization.

One factor that seems to contribute to the departures of early hires who’ve had leadership roles at the social network: They can easily sell their shares in Facebook without having to wait for the company to go public.

Jackie Cohen wrote the opinion portions of this post.