Kevin Colleran HeadshotFacebook recently won plaudits as the best tech employer but that doesn’t stop people leaving. Liz Gannes at GigaOm has written a fascinating post charting all the early employees now leaving Facebook and the various reasons why. Although Facebook is now six years old, the notable fact is that the company is yet to go public so early employees have not been able to cash out stock options in an IPO.

Apparently Kevin Colleran, the company’s first ad sales person, is now the longest-serving Facebook employee after Mark Zuckerberg. Other early employees, such as Chris Hughes, Dustin Moskovitz and Adam D’Angelo have left and founded their own start-ups.

Recent departures reportedly include Aaron Sittig, who is credited with creating the concept of tagging Facebook friends in photos; Chris Putnam, the creator of Facebook Video; Ruchi Sanghvi, the company’s first female engineer, announced the Facebook news feed back in 2006; and Ezra Callahan, who joined in 2004 as the company’s first product manager. Also this year the company has lost Yishan Wong, who joined in 2005 and was director of engineering, and Kate Losse, who joined in 2005 and was product manager for internationalization and localization.

Many former employees are traveling or relaxing, while others have started their own start-ups. The decision to exit pre-IPO may have been eased by the equity stake taken by Digital Sky Technologies in May last year. Gannes speculates that some employees may have been frustrated with the fact that the management team is mostly made of external hires, many of them formerly from Google.

The departure of early employees with stock options may help ease the pressure for Facebook to go for an IPO, leaving Zuckerberg and senior management more free to make that decision when the timing is right for the company and market conditions are buoyant. On the other hand, it does mean a loss of the early start-up culture and entrepreneurial spirit. Perhaps that’s why most of Facebook’s recent acquisitions have involved stock transfers and have been described as “expensive hires”. There have been several over the past few months but the most recent was ChaiLabs yesterday.

Photo: Kevin Colleran, director of national sales at Facebook is the company’s longest-serving employee.