SAN FRANCISCO: Social networking site Facebook officially has 500 million users, the company has announced. The milestone means that the six-year old website now reaches eight percent of the planet's population, just 18 months after it passed the 150 million user mark. Last month Facebook founder and CEO Mark Zuckerberg said there is a "good chance" that the social networking site could boast one billion users within three to five years. Facebook has continued adding users at a record-setting pace despite growing concerns about the privacy policies of a site that has more data on its users than any other website. Facebook marked the milestone with the launch of a special section in which users are encouraged to post their personal stories about how Facebook has affected them. "Half a billion is a nice number but the number isn't what really matters here. What matters are all of the stories we hear from all of you about the impact your connections have had on your lives," Zuckerberg said in a video message. "Instead of focusing on numbers, we want to help people around the world hear about these stories for themselves, and we want to let you tell your own story."