• by Mark Walsh  @markfwal, April 8, 2009

That was fast. Facebook has hit 200 million active users only seven months after the social network hit 100 million users and 90 days after reaching 150 million. On average, Facebook has added 500,000 new members a day since late August, according to the blog Inside Facebook.

If it were a country, the site would be the fifth most populous, larger than Brazil and Japan. In a blog post Wednesday about the milestone, Facebook co-founder and CEO Mark Zuckerberg wrote: "Both U.S. President Barack Obama and French President Nicholas Sarkozy have used Facebook as (a) way to organize their supporters. From the protests against the Colombian FARC, a 40-year-old terrorist organization, to fighting oppressive, fringe groups in India, people use Facebook as a platform to build connections and organize action."

To mark the occasion, Facebook has begun a campaign selling a collection of virtual gifts for the benefit of 16 charitable and advocacy organizations including UNICEF and the UN Refugee Agency's "Gimme Shelter" campaign. It also set up a site for people to share stories about how Facebook helped them effect change or connect with a distant relative.

Facebook's biggest challenge remains monetizing its ever-expanding audience, 70% of which is outside the U.S. Market research firm eMarketer projected that Facebook would break $200 million in revenue last year -- at $210 million -- but that figure came after twice cutting its original estimate of $305 million due to the recession.

The company last week said it was pleased with its financial performance. According to an internal memo cited by D: All Things Digital, Facebook expects to increase revenue 70% in 2009 and be cash flow-positive in 2010.

Adding a half a million new users each month becomes costly, however. Facebook is reportedly trying to raise another $100 million in debt financing to lease more servers to keep pace with its torrid growth. Facebook has also hinted that an IPO is in its future.