Google+, Google's challenge to Facebook, is adding 625,000 daily users and already may have as many as 62 million signed up, unofficial statistician Paul Allen claimed.

If the rate continues, the social networking alternative to Facebook - which claims as many as 800 million users - could exceed 100 million users as early as Feb. 25, reports carried by C-net said.

Allen, no relation to the Microsoft co-founder and owner of the Seattle Seahawks football team and Portland Trailblazers basketball team, suggested growth for Google+ could accelerate into 2012, especially after the Mountain View, Calif.-based search engine completes its $12.5 billion acquisition of Motorola Mobility, the smartphone maker.

Google doesn't report daily or weekly figures but does so quarterly. When it reported third-quarter results, it had 40 million users, all signed up in one quarter.

Google shares rose $3.07 to $643.43 in early Wednesday trading.

Facebook, based in Palo Alto, Calif., has not provided recent updates but maintains its 800 million subscriber number. The company will be required to report financial results and other data for the first quarter of 2012 because it now has more than 500 shareholders.

That could mean Facebook will schedule an initial public offering or report financial results to the U.S. Securities and Exchange Commission. Besides individuals such as founding CEO Mark Zuckerberg, Facebook's shareholders also include Goldman Sachs, Russia's Digital Sky Technologies and Microsoft.

Google's August 2004 IPO was co-managed by Morgan Stanley and Credit Suisse First Boston. It raised $1.67 billion and closed its first trading day with a market value of $23 billion. Based on the current price, Google's value has risen to $208.3 billion.