NEW YORK (AP) -- Facebook has acquired the start-up behind the popular fitness tracking app Moves as it expands beyond its namesake service into a company with multiple, differentiated mobile apps.

The world's largest online social network will keep running the service separately.

Menlo Park, Calif.-based Facebook said Thursday it bought ProtoGeo Oy, the Finnish company behind the app, for an undisclosed sum.

Launched in 2013, the Moves app has been downloaded 4 million times on Android phones and the iPhone. It lets people automatically track their runs, walks or bike rides and plots the user's routes on a map.

To move beyond its core service, Facebook is developing and acquiring different kinds of apps. This year, it announced a $19 billion deal for mobile messaging service WhatsApp and launched the news reader app Paper.

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