SAN FRANCISCO (CNNMoney) -- Three behind-the-scenes power players have left Twitter, the latest in a series of departures that are reshaping the micro-messaging site.
Board members Fred Wilson and Bijan Sabet, two of Twitter's earliest investors, are stepping down, the company said Friday. On Thursday, Twitter Chief Scientist Abdur Chowdhury confirmed that he is leaving the company.
"Bijan Sabet and Fred Wilson both played important and greatly appreciated roles in our success," Twitter said in a written statement. "Both saw what Twitter could become before most anyone else. We look forward to their continued input as both investors in the company and passionate users of the product."
Twitter recently completed a massive $800 million funding round, half of which went to cash out part of the holdings of some early investors, including Wilson's firm, Union Square Ventures. USV kept some of its stake in Twitter.
Twitter's $400 million war chest will help the five-year-old company tackle a problem of growing urgency: Building a sustainable business on top of its widely used, free platform. In a "State of the Union" talk last week, CEO Dick Costolo publicized the latest Twitter stats: 100 million active users log in at least once a month.
Costolo took over in October as the company's CEO, assuming the reins from co-founder Evan Williams, who planned to step back and focus on product development. But just a few months later, Williams ceded that role to once-exiled co-founder Jack Dorsey, who now juggles his Twitter duties with his CEO role at payments venture Square.
Williams and Twitter's third co-founder, Biz Stone, have faded away from active involvement at Twitter. In June, they launched a new venture: Obvious Corp., an incubator for companies focused on "building systems that help people work together to improve their lives and the world." 
