Facebook on Thursday began rolling out a feature allowing users of its mobile app to use smartphone location to discover friends near them.

The optional "nearby friends" feature "helps you discover which friends are nearby or on the go," said product manager Andrea Vaccari in a blog announcement.

"If you turn on Nearby Friends, you'll occasionally be notified when friends are nearby, so you can get in touch with them and meet up," Vaccari said.

"For example, when you're headed to the movies, Nearby Friends will let you know if friends are nearby so you can see the movie together or meet up afterward."

With the feature, Facebook takes a page from other location-based services including the network Foursquare, numerous dating apps and the recently launched social network aggregator SocialRadar.

With the Facebook feature, Vaccari said, "You can choose who can see if you're nearby (for example: your friends, close friends, or a specific friends list) and you can turn it on and off at any time."

He added that the location sharing must be mutual: "You and your friends both have to turn on Nearby Friends and choose to share with each other to see when you're nearby. Your friends will only be able to see that you're nearby if you share this info with them and vice versa."

Facebook will also allow users to share a precise location with the particular friends for a set period of time.

"When you share your precise location, the friend you choose will see exactly where you are on a map, which helps you find each other," said Vaccari.

Facebook had an estimated 1.23 billion users at the end of December, and more than one billion who use the social network on a mobile device.

The "nearby friends" feature will be available for Android and iPhone users in the United States over the coming weeks.