Google+ users reach 20 million in 3 weeks

After only three weeks, Google+, Google's answer to Facebook, has reached 20 million members, according to comScore extrapolations. Adweek reports that the invitation-only version of Google+ has not been marketed yet leveraging Google.com's powerful 1-billion monthly visits.

"I've never seen anything grow this quickly," said Andrew Lipsman, vice president of industry analysis at comScore, quoted in the Wall Street Journal. "The only other site to reach this kind of user accumulation is Twitter back in 2009. But it happened over several months," he said.

comScore employs a panel-based methodology, and claims 2 million people are on their global panel. The research company then extrapolates from the panel numbers and projects a global usage number. Comparatively, Twitter has 200 users and Facebook has 750 million users.