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Shares of Facebook reached a new low on Friday after another investment firm cut the social media company's target price and news that the co-founder is selling his shares.

BMO Capital Markets cut Facebook's price target to $15, down from $25, saying investor views of the company are lower.

Facebook's stock dropped 5.39 percent to $18.06 about a half hour before Friday's close, less than half of its offer price of $38 in May.

When you own hundreds of millions of shares of a company, is it significant if you sell 150,000 shares a day? If it's just one percent of your holdings, maybe not. Dustin Moskovitz, company co-founder has sold 1.35 million shares for proceeds of $26.2 million, at a stock price of $18.79 to $20.08, the Associated Press reported.

Moskovitz, who went to Harvard with co-founder Mark Zuckerberg, was Facebook's chief technology officer then vice president of engineering. Moskovitz left Facebook in 2008 to start workflow web application company Asana.

Moskovitz has been disclosing his sales every three days with the Securities and Exchange Commission.

Moskovitz's first large sale of shares was recorded on Aug. 17, a day after Facebook's lockup period ended, allowing early investors to sell their shares.

A spokeswoman for Facebook declined to comment.

Moskovitz could not be reached for comment.