Facebook who? On the same day the tech world awaits the social network's IPO filing, fledgling rival Google+ is set to break 100 million users, according to one analyst.

Paul Allen, a Google+ watcher, says the network will hit 100.8 million users by Wednesday evening. Google's most recent figure for Google+ was 90 million, which Larry Page announced on Jan. 19.

In a blog post (on Google+, of course), Allen noted that the network has grown more than 10% in that two-week period. Allen, the founder of Ancestry.com, takes an unusual approach to come by his estimates: He and his staff run hundreds of queries on surnames they’ve been tracking since July and then extrapolate the size of the network. His method seems to work: Allen's numbers are often very close to figures that Google cites a few days later.

Allen has also predicted that Google+ will hit 400 million users by year's end. That's half the number that Facebook currently claims.

A few factors may have contributed to Google+'s recent growth: Google opened the network up to teens last week and Google plus Your World, a program introduced last month that integrated Google+ into the company's search results, may have increased visibility for the platform.

Facebook's recent moves may have also prompted some to check out the platform. For example, the company's introduction of Timeline has rankled some users.

What do you think? Are you spending more time on Google+? Sound off in the comments.