Major investors of public companies are required to disclose when they buy and sell stock. A few have done so for Facebook Inc. in recent days, according to filings with the Securities and Exchange Commission:

— Monday: Disclosure that Peter Thiel, a member of Facebook's board, sold about 20 million shares at $19.27 to $20.69 each on Aug. 16 and 17. That amounted to nearly $400 million. Thiel is managing partner at The Founders Fund and a co-founder of PayPal. He had been subject to a lock-up period restricting sale of those shares until Aug. 16. As one of Facebook's initial investors, he first invested $500,000 in the company in 2004. He sold 16.8 million shares in the company's May initial public offering for about $640 million. With the most recent sales, Thiel has now sold most of his stake in the company.

— Tuesday: Disclosure that Facebook co-founder Dustin Moskovitz shed 450,000 shares on Aug. 17, 20 and 21 for $18.79 to $20.08 each. Proceeds came out to nearly $9 million. Moskovitz was CEO Mark Zuckerberg's Harvard roommate when they founded Facebook in 2004. He left Facebook in 2008 and started Asana, whose software helps manage projects. Moskovitz, who did not sell any stock in Facebook's IPO, still owns more than 133 million shares. Based on the filing, he could sell 7 million more shares he converted from Class B to Class A.