Facebook's future seemed bright when Microsoft invested $240 million for a 1.6 percent stake in the company back in October. But as the social network struggles to profit from advertising and find a monetization model, many have scoffed at the company's $15 billion estimated value.

Now, Facebook bigwigs, including CEO Mark Zuckerberg, are selling off shares, and at prices that value the company at far less than $15 billion, according to Business Week.

Laurence Albukerk, a Silicon Valley stockbroker, told Business Week that among the dozens of Facebook employees selling their stock, several are selling for a $5 billion valuation, with some going as low as $3.75 billion.

Morale at Facebook headquarters reportedly took a plunge when word leaked that Zuckerberg sold stock, and now the company is letting employees sell stock this fall in a one-time program. Employees will also be able to buy shares in the company, according to Silicon Alley Insider.