Facebook chief executive Mark Zuckerberg introduced the new "Graph Search" feature at a press event in California.
He said: "Every piece of content has its own audience; most content is not public; you can only search for content that has been shared with you".
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Kurt Cochran and his wife Melissa had been visiting London from the US to celebrate their 25th wedding anniversary and were due to fly home.
The Government has previously described the new coin - which enters circulation tomorrow - as "harder to counterfeit than ever before".
The European bloc said that Russia should release hundreds of people it arrested at anti-government protests and rallies.