ComScore said Google+ has racked up more than 20 million users, including 5 million in the U.S., in the first three weeks since the search engine launched the social network as an alternative to Facebook.
The researcher culled estimates from unique visitors who arrived at Google+ from June 29 through July 19, said Andrew Lipsman, vice president of industry analysis at comScore.
"As of July 19, comScore showed Google+ at just about 20 million visitors worldwide, an extraordinary number in just its first three weeks," Lipsman said, adding that the figure represents an increase of 82 percent from the previous week and 561 percent vs. two weeks prior."
The Google+ U.S. audience paced the field, surpassing 5 million visitors, up 81 percent from the previous week and 723 percent from two weeks earlier.
But Google+'s global growth is impressive to Lipsman, who noted that while the U.S. leads in Google+ audience, India is No. 2 with 2.8 million visitors. The U.K. has (867,000 visitors), Canada (859,000 visitors) and Germany (706,000 visitors) rounded out the top five.
The Google+ numbers could be even greater because comScore didn't count visitors from mobile phones. Lipsman said he excluded visits from iPhone and Android smartphone users, limiting estimates to those who navigated to plus.google.com pages from home and work computers.
He also did not take into account Google+ usage that occurs through the Google+ tool bar that crests atop most Google pages these days.
Even so, Lipsman believes the growth may be unprecedented as new Website destinations go.
"It would be difficult to think of many sites that reached such a large number in such a short period of time," Lipsman said, adding that Google's built-in user base of more than 1 billion searchers clearly helped. "There is clearly potential to convert a high number of users to its new social tool-even if it is still invite-only.
However, Lipsman also cautioned that while the early start is promising, the Website will have to work hard to keep people active and engaged on the network.
One of the ways Google missed the mark there is in its botching of a business pages launch.
That is, such pages are not yet supported despite a massive outcry from "tens of thousands" of brands that want to market themselves on the new social network, said Christian Oestlein, the product manager responsible for Google+ advertising.
"Your enthusiasm obligates us to do more to get businesses involved in Google+ in the right way, and we have to do it faster," Oestlein acknowledged. "As a result, we have refocused a few priorities, and we expect to have an initial version of businesses profiles up and running for everyone in the next few months."
Oestlein is selecting business partners for a test period this week. Meanwhile, Google (NASDAQ:GOOG) has suspended such accounts by the blog Mashable, program Sesame Street and others because Google+ is not business-ready.
Vic Gundotra, Google's vice president of engineering overseeing Google+, said in response to Search Engine Land Editor Danny Sullivan's open letter on Google+: "We should have anticipated brands and people who want a following would be very frustrated when we didn't have proper profile support."
"This is my fault...We prioritized making a great experience for people first. None of our internal models showed this level of growth. We were caught flat-footed."
Gundotra added that Oestlein and his team "are doing all we can to accelerate the work to properly handle this case."