After overtaking Microsoft's Windows Live Profile in Portugal and Mexico in early 2010, Facebook eclipsed StudiVZ in Germany and Google's Orkut in India later that year, and soon unseated Hyves in the Netherlands, according to metrics firm comScore. Now Facebook is poised to triumph in what has been viewed as its ultimate popularity contest, with comScore indicating the network is likely to dethrone Orkut in social media-mad Brazil when its December data is released.

Facebook's relentless spread is a vindication of founder and CEO Mark Zuckerberg's growth-first principle, under which the social network has focused primarily on adding users, not building revenue, since its beginning. Facebook will surpass 1 billion users in the next few months, analysts say, and that population will be a huge asset it can tout to investors as the company prepares for an initial public offering of stock as soon as spring.

"It's been really surprising to us to see how quickly Facebook has grown, not just in Western countries or English-speaking countries, but pretty much around the world," said Carmela Aquino of comScore. "I think part of it is the network effect -- when you have a big enough mass of people beginning to jump on a social network, it's only a matter of time that their friends get on the same network, and it starts to spread."

Facebook is now used by more than half the population in the U.S. and a number of other countries, according to analytics company Socialbakers, but its growth is slowing in North America and much of Europe as it approaches a saturation point. Still, as Facebook prepares for its IPO, the Menlo Park, Calif.-based social networking company's massive expansion in...