Facebook (Nasdaq: FB), operator of the world’s largest social network, is rolling out a feature that will let users pay to promote friends’ posts on the website as it seeks new sources of revenue.

The tool expands on a service introduced last year that lets users pay to promote their own posts. The new service will cost about $7 in the U.S., though prices may vary, the company said in an e-mailed statement Thursday.

Sluggish profitability growth and sagging shares are pressuring Facebook to find new ways to generate more revenue from its 1.1 billion members. In the past year, the company has announced mobile-advertising, tools for marketers on desktops and a feature for users to send friends gifts via the site.

“If your friend is running a marathon for charity and has posted that information publicly, you can help that friend by promoting their post to all of your friends,” the company said. “If your friend is renting their apartment out and she tells her friends on Facebook, you can share the post with the people you and your friend have in common so that it shows up higher in news feed and more people notice it.”

The tool for promoting friends’ posts will be gradually introduced globally, Facebook said. The social network already operates a service that lets companies pay to promote posts.

To safeguard privacy, promoted posts will be visible only to users permitted to see the original messages.

Facebook rose 2.1 percent to $28.50 at Thursday’s close in New York. Shares of the Menlo Park, California-based company have declined 25 percent since an initial public offering in May.