Facebook reportedly now has 750 million monthly active users, but you won't hear about the milestone from the company itself. The new number comes from a source close to the social network, cited by TechCrunch. Facebook is of course saying it doesn't have anything to announce in regard to its user base.
On January 5, 2011, a Goldman Sachs report to potential investors leaked out, and quoted 600 million users. So unofficially, Facebook has over 600 million users. Unofficially, however, it still has over half a billion users.
On July 21, 2010, Facebook CEO Mark Zuckeberg announced the site had passed the 500 million user mark. Facebook has obviously been growing since then, but it has not made an announcement in regards to the size of its userbase for almost a year.
The next official number may be revealed in the coming months. The Facebook f8 (pronounced "fate") conference is a yearly event held by Facebook that takes place in San Francisco, California; the 2011 edition of f8 will most likely be held in August 2011. The company is going public next year, possibly as soon as Q1 2012. Either would be a good time to announce a new milestone, say 1 billion users?
It's possible that Facebook is waiting until it hits the 1 billion mark before making an official announcement, and hoping that the timing works out with its next conference or its initial public offering (IPO). After the 1 billion mark, the next milestone will be passing India, and then China. If Facebook was a country, it would be the world's third largest, by population.
Plenty of websites only report cumulative users, which does not take into account inactive accounts. Facebook's user count metric is much better as it is defined as a user who has logged in within the last 30 days. Still, this does not eliminate the issue of one person having multiple accounts.
Recently, there have been numerous reports about Facebook's user base. Last month, Socialbakers reported that the site had around 700 million users. Earlier this month, Inside Facebook reported that the number was actually 687 million users (and that numbers in the US and Canada were falling).
Both statistics are of course just estimates, based on third-party companies like Quantcast and/or Facebook's advertising tools. At the time, Facebook made a point to debunk these numbers, but didn't provide an official one.
"From time to time, we see stories about Facebook losing users in some regions," a Facebook spokesperson said in a statement. "Some of these reports use data extracted from our advertising tool, which provides broad estimates on the reach of Facebook ads and isn't designed to be a source for tracking the overall growth of Facebook. We are very pleased with our growth and with the way people are engaged with Facebook. More than 50% of our active users log on to Facebook on any given day."