
Ancestry.com founder Paul Allen, who has been keeping track of Google+ user numbers via his ‘uncommon surname’ method, wrote on Google+,”On September 9, our model showed 28.7 million users. This morning, our model shows 37.8 million users, with most of the growth coming in the last 2 days.”
“By adding a fudge factor (see below) to account for private user profiles and for non-Roman surnames (both of which are totally overlooked by our surname counting model), my current estimate is 43.4 million users,” he said.
This was not the exact count but we can think it as approx count of users. So we can guess that Google+ has 50 million users.