Facebook Inc., owner of the world’s largest social network, said retailers have increased use of an advertising tool that lets them send promotions to their existing customers.

The number of marketers using Facebook’s Custom Audiences tool in the third quarter rose almost 75 percent from the prior period, the company will say in a blog post today.

Facebook has been tailoring its offerings for retailers ahead of the holiday shopping season, in a push to attract more advertising spending with its member base of more than 1 billion people. The Menlo Park, California-based company is asking marketers to use Custom Audiences to promote gift ideas and sales to consumers who are already customers, or to acquire new shoppers by excluding existing customers from campaigns.

U.S. online holiday sales are projected to increase as much as 15 percent to $82 billion this year, more than three times faster than the total estimated retail gain of 3.9 percent to $602.1 billion, according to the National Retail Federation.