Facebook Inc. Chief Operating Officer Sheryl Sandberg and a trust in her name sold $14.2 million of stock in the operator of the world's largest online social network.

Sandberg and the trust sold 508,118 shares at prices averaging about $28, according to a Jan. 4 Securities and Exchange Commission filing. The sales took place a day earlier.

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The transactions follow the end of lockup periods for shares sold in the Menlo Park, California-based company's initial public offering in May. The stock has tumbled 23 percent since the $16 billion sale, the biggest IPO for an internet company.

Sandberg has a net worth of about $500 million, according to Bloomberg Billionaires. She owned 1.65 percent of Facebook following the Jan. 3 sales, according to data compiled by Bloomberg. The internet company rose 2.3 percent to $29.42 in New York trading Monday.