Facebook Inc Chief Operating Officer Sheryl Sandberg sold $3.75 million worth of stock in the company on Tuesday, her second stock sale since trading restrictions on insiders expired last week.

Sandberg sold roughly 176,000 Facebook shares for an average price of $21.24 on Tuesday, according to a regulatory filing on Thursday. Sandberg still owns nearly 19 million vested shares of Facebook, the world's No.1 Internet social network, according to the filing.

Last week, Sandberg sold roughly $7.4 million worth of Facebook stock. Facebook General Counsel Theodore Ullyot and Chief Accounting Officer David Spillane also sold millions of dollars worth of shares last week. All the Facebook executives' sales were part of pre-arranged stock trading plans.