Co-Founder of Facebook to Leave Firm

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Dustin Moskovitz

Mr. Moskovitz founded the social-networking Web site with Mark Zuckerberg, who is now Facebook's chief executive, while they were both students at Harvard University several years ago.

Justin Rosenstein, a Facebook engineering manager, will also leave the company to join Mr. Moskovitz in starting a new software business. In a message left on Mr. Moskovitz's Facebook page, the two said they have been working on software for business users and wanted to incorporate the software into Facebook.

"But at some point it became clear that doing so wouldn't be good for Facebook or for us," he wrote. Mr. Moskovitz wrote that he sees the new venture as complementary to Facebook.

Several other executives have left Facebook over the past 18 months, including Owen van Natta, who served as chief revenue officer and chief operations officer; Adam D'Angelo, its former chief technology officer; and Matt Cohler, vice president of product management.

"Dustin has always had Facebook's best interest at heart and will always be someone I turn to for advice," said Mr. Zuckerberg in a statement.