After falling as low as $18.55, Facebook shares recovered a little, closing at $18.79, down 19 cents, or 1 percent.
Moskovitz, 28, a former Harvard roommate of Facebook CEO Mark Zuckerberg who runs his own company, Asana, advised the U.S. Securities and Exchange Commission that he sold 150,000 shares on Sept. 4 and Sept. 5 and an additional 2.7 million shares on both Sept. 6 and Sept. 7.
The SEC filings show that as of the close of business Friday, Moskovitz is no longer a shareholder of Facebook's Class A shares. However, he remains a shareholder of the company's Class B shares.
Moskovitz previously sold about a million shares in August. The cumulative sales have netted the young executive more than $143 million.
Asana, also in Menlo Park, Calif., is a social networking site intended for business users.
Zuckerberg, 28, controls the majority of both classes of Facebook shares, for about 58 percent of the total.
Although he sold shares in the company's May 17 initial public offering for the official purposes of paying capital gains taxes, he pledged not to sell any more shares for at least a year, as did directors Marc Andreesen, a venture capitalist who co-founded Netscape and now is a director of Hewlett-Packard Co. (NYSE: HPQ) and Donald Graham, chairman of the Washington Post Co. (NYSE: WPO).
Facebook's loss since the May IPO is now 51 percent.