NEW YORK (CNNMoney) -- The Google+ social network has topped 60 million users, according to Ancestry.com founder Paul Allen, who also made the bold prediction late Tuesday that Google+ would reach 400 million users by the end of 2012.
Allen, who calls himself the "unofficial statistician" of Google+, runs hundreds of queries on various surnames on the social network each week. He has been tracking those names since Google first announced that Google+ had reached 10 million users in July.
Google+, the company's answer to Facebook, got off to a roaring start, hitting the 10 million mark in just two weeks -- and that was even before the site was open to the public.
But growth had tapered off, taking three months to reach 40 million users, according to Google's numbers.
Google's hasn't given a more recent count. But Allen has seen a rapid resurgence, estimating that the service hit 62 million late Tuesday.
"It may be the holidays, the TV commercials, celebrity and brand appeal, or positive word of mouth, or a combination of all these factors, but there is no question that the number of new users signing up for Google+ each day has accelerated markedly in the past several weeks," Allen wrote on his Google+ page.
Google's (GOOG, Fortune 500) social network is now adding 625,000 users each day, Allen said.
At that pace, Google+ would reach nearly 300 million users by the end of 2012. But Allen believes that growth will accelerate, enabling it to hit 400 million.
There's one crucial missing piece in Allen's analysis: He only cites the total number of people who have signed up for the network, not the number of people who actually use it. People may sign into the service to check it out and never use it again.
Facebook, by contrast, reports that it has 800 million "active users," which are those users that have viewed a Facebook page or have used an application. Half of all Facebook active users log onto the social network in any given day, the social network says.
Google entices users to sign up in its newly redesigned home page, by making Google+ the first option in an ever-present pull-down menu -- an option that sits right above search. It's unclear how many sign up but then never actually use Google+.
The technology and advertising industries alike are watching Google+ very closely, which could yet prove to be a sizable alternative to Facebook. The project is very important to Google, which is trying to overcome its past miscues in the social networking space.
More people visit Google's network of websites than Facebook each month, but Facebook is killing Google in categories that advertisers care most about: Time spent and pages viewed. 
