FriendFeed will initially continue to operate on its own, but it is expected it will later be folded into Facebook. It allows people to share content, make comments and see what their friends are doing in real-time on a host of social media sites from blogs, to Twitter and social book marking sites like Digg as well as RSS feeds.
Mark Zuckerberg, Facebook founder and CEO, said: "Since I first tried FriendFeed, I've admired their team for creating such a simple and elegant service for people to share information.
"As this shows, our culture continues to make Facebook a place where the best engineers come to build things quickly that lots of people will use."
The acquisition further expands Facebook's real-time web capabilities, which is one of the fastest growing areas of the web, and makes up in some ways for its failure to agree a deal to buy rival Twitter last year.
Twitter rejected an offer valued at $500m from the social media market leader in November 2008 after the two could not agree on the value of Facebook's stock.
According to a report in the Wall Street Journal, Facebook has paid around $50m in cash and stock for FriendFeed, which was started by four ex-Google engineers.
As much as $15m of that has been paid in cash with the rest in Facebook stock. The stock part of the deal is valued at around $32.5m and is based on the current $6.5bn valuation of Facebook.
Bret Taylor, FriendFeed co-founder, and previously the group product manager who launched Google Maps, said: "Facebook and FriendFeed share a common vision of giving people tools to share and connect with their friends.
"We can't wait to join the team and bring many of the innovations we've developed at FriendFeed to Facebook's 250m users around the world."
Paul Buchheit, another FriendFeed co-founder, who worked on Gmail at Google, said: "As we spent time with Mark and his leadership team, we were impressed by the open, creative culture they've built and their desire to have us contribute to it.
"It was immediately obvious to us how passionate Facebook's engineers are about creating simple, ground-breaking ways for people to share, and we are extremely excited to join such a like-minded group."
Taylor and Buchheit founded FriendFeed along with Jim Norris and Sanjeev Singh in October 2007 after all four played key roles at Google. The company is based in Mountain View, California and has 12 staff.
Taylor told the WSJ that both companies have been "casually" talking about joining forces for a while, but that talks really accelerated "in the past week".
Facebook will integrate FriendFeed's powerful search architecture into its own real-time search platform, which it unveiled today.
The improved Facebook search, two months in the making, is a direct strike at Twitter's lucrative real-time search platform.
Users can now search Facebook to find breaking news, bringing in results from friends' status updates, conversations, photos, links and video -- all powered by Microsoft's Bing.
Previously, users were only able to search through profiles and groups.
Facebook's 250m users puts the social networking site in the same league as Google, which has also expressed interest in launching a real-time search engine.
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