Social networking leader Facebook said on Wednesday its user base has swelled to more than 400 million and shows no sign of slowing.

Mark Zuckerberg, Facebook's chief executive, also unveiled new features for the world's No. 1 Internet social network, as the company looks to make it easier for outside developers to build and interact on the growing Facebook platform.

Facebook will offer an enhanced ability to share content and personal information across outside Web sites.

Zuckerberg said Facebook is growing at a faster rate than ever before and is building toward a future where everything can be social and more personalized.

Starting Wednesday, Facebook users can click on a simple like button featured next to content on popular sites including CNN, ESPN and Yelp, and share that information back to their Facebook profile in a more comprehensive fashion than with the share button currently used on many sites.

Those sites in turn will be able to display content from those within a Facebook users' network. For example, a box on CNN.com would show that three friends liked a certain story.

Zuckerberg outlined the plans during his keynote address at f8, Facebook's annual developers' conference, held in San Francisco.

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

(Reporting by Gabriel Madway, editing by Maureen Bavdek)

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