Facebook's user base is growing at its fastest rate ever, the online social network company said on Wednesday as it rolled out features that link the company's platform more tightly with outside Web sites.

Facebook's open graph would let people see information tailored to their lives and interests wherever they are on the Web, the company's chief executive Mark Zuckerberg said at the f8 conference in San Francisco.

The idea, Zuckerberg said, is to make Facebook the center of the increasingly social and more personalized experience that people encounter when they use the Internet. Facebook also wants to make it easier for other websites to share information across Facebook's user base of more than 400 million people.

We're building toward a Web where the default is social, every application and product will be designed from the ground up to use real identity, he said.

Facebook users would be able click on a like button next to content on sites such as Time Warner Inc's CNN and Walt Disney Co's ESPN, and share the information on their Facebook profiles in a better way than the share button that many sites use.

Those sites in turn could display content from a Facebook user's network. For example, a box on CNN.com could show that three friends liked a certain story.

Facebook has also partnered with review site Yelp and music discovery service Pandora, to enable more widespread sharing of users' preferences across those sites.

In addition, Facebook and Microsoft, which owns a small piece of the social network, are launching a document creation and sharing application, based on Office 2010, that can be accessed through Facebook and an outside site.

Facebook, which has faced criticism for sharing too much user information, deflected questions about privacy concerns.

In a press conference following the keynote, Zuckerberg said applications on third-party sites will share no more information than before.

I think what this actually means is that people are going to be sharing less of their information when they don't need to around the Web, he said.

GROWING FAST

Since its creation in a Harvard dorm room in 2004, Facebook has emerged as one of the Internet's most popular destinations and is increasingly challenging established Web powerhouses like Yahoo Inc and Google Inc.

Facebook is the fourth-most visited site in the United States, and displaced Google in January to become the top U.S. site by total number of Web pages viewed.

Facebook's event comes a week after rival social networking sensation Twitter held its developer's conference in San Francisco, and announced that it had signed up more than 100 million users -- marking the first time the company has revealed its number of users.

In September, Facebook said that it had recently turned free cash flow positive, meaning that it makes enough money to cover operating costs and capital spending.

Facebook director Mark Andreessen also told Reuters last year that the company would surpass $500 million in revenue in 2009.

Last year, Facebook received $200 million in funding from Russian Internet investment firm Digital Sky Technologies, in a deal that pegged the value of Facebook's preferred shares at $10 billion. DST also bought more than $100 million of common shares directly from Facebook shareholders, valuing Facebook's common shares at $6.5 billion.

(Reporting by Gabriel Madway. Editing by Maureen Bavdek and Robert MacMillan)

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