Facebook announced on its official blog that the number of people using the social-networking site had reached 500 million. The figures mean one in every 14 people on the planet has now signed up to the online community.

"This is an important milestone for all of you who have helped spread Facebook around the world. Now a lot more people have the opportunity to stay connected with the people they care about," Facebook chief executive Mark Zuckerberg said in his 500 Million Stories blog post.

To celebrate, the California firm launched an application that lets members "tell the incredible stories of the moving and interesting ways they've used Facebook".

Instances given by Mr Zuckerberg included a US woman using the service to battle breast cancer and NATO Secretary General Anders Fogh Rasmussen jogging with Facebook fans during his term as Denmark's prime minister.

"Our mission at Facebook is to help make the world more open and connected," Mr Zuckerberg said.

"Stories like these are examples of that mission and are both humbling and inspiring. I could have never imagined all of the ways people would use Facebook when we were getting started 6 years ago."

Mr Zuckerberg, 26, who co-founded Facebook in 2004 while in Harvard, is said to be the world's youngest billionaire.

The company reported $US800 million ($910 million) in revenue in 2009 and is foreseen to generate over $US1 billion this year.

In March, the Wall Street Journal announced that Facebook investors anticipated the company going public in 2011 with a market capitalization of $US35 billion to $US40 billion.

The Social Network, a motion picture directed by David Fincher about Facebook and its founder, is set for release in October.