Facebook has announced it is creating a new search engine for content uploaded by its users.

Speaking during a "mystery event" at the company's headquarters in Menlo Park, California, the social media behemoth's founder and chief executive Mark Zuckerberg unveiled the service, dubbed Graph Search.

The announcement came after speculation the company would seek to bounce back from its poor performance since becoming a public company last year with a smartphone gadget or web search engine of its own.

But Mr Zuckerberg, 28, stressed that the new product was "very, very different" to the web search engines operated by tech heavyweights such as Google.

Facebook's new tool will allow its one billion members to search for people, photos, places and other content that their friends have already shared on the social network.

But it will also be "integrated" with Microsoft's Bing search engine, with searches that are not available on Graph Search redirecting to Google's main internet search competitor.

Asked whether the move targeted Google, Mr Zuckerberg said: "You know, I would love to work with Google - when we did our Bing web search integration we were very public about the fact this wasn't something we were trying to do with Bing.

"We want to make web search social in general."

Mr Zuckerberg said the new search tool would be rolled out "very slowly", starting with a beta version available to a limited number of users immediately.

It came after Facebook suffered what Mr Zuckerberg described as a "rough cycle" since becoming a public company amid wild expectation last May.

After starting at a per-share price of 38 dollars, the stock's performance sagged, but had picked up in recent weeks amid speculation over today's announcement.

Andreas Pouros, chief operating officer at Greenlight, a digital marketing agency, said Graph Search was "innovative and powerful" but would do little to allay investors fears over Facebook's "commercial focus".

He said: "Many had expected Facebook would have launched a new mobile phone or thrown down the gauntlet to Google and challenged the company in web search supremacy, neither of which happened.

"Web search is a touchy subject as everyone knows that it is a hugely lucrative market, and one Facebook was expected to enter.

"Graph Search may well be a precursor to that but I fear investors will suspect that it is too little progress."

The company will release its quarterly earnings figures on January 30.

Questions also arose over how the new tool will affect Facebook users' privacy.

But Facebook insisted that the feature included an opt-out option to keep users' contents out of searches.

Chris Edwards, an electronics correspondent for Engineering and Technology magazine, said: "People don't really think about privacy and what they are uploading until they see stories about abuses.

"But if you look at some of the features available on Facebook, it's almost like a stalker's toolkit."

Mr Edwards said that how users perceived potential privacy encroachments and reacted to increased levels of targeted advertising would determine the new service's success.

Facebook photo-sharing service Instagram ran into trouble last month after an update in its terms and conditions sparked concerns that it would claim ownership over users' pictures and sell them to advertisers without permission.

Instagram insisted that it was not claiming ownership rights and had no plans to sell pictures to advertisers.

Mr Zuckerberg first started Facemash in 2003 while he was a computer science and psychology student at Harvard.

By 2007, the site's evolution into the worldwide Facebook phenomenon had made the then 23-year-old one of the world's youngest self-made billionaires.