Jul 20, 2011 09:21 GMT  ·  By

Google+ has certainly generated a lot of hype and interest. This was based mostly on empirical evidence and estimates until CEO Larry Page revealed that the social network had 10 million users in the first two weeks.

Now, a week later, Google+ may be hitting 18 million users, a huge number, but the growth rate is actually slowing down, unsurprising for any new product which is starting to go past its initial hype.

Paul Allen, an entrepreneur and founder of Ancestry.com, has been keeping track of Google+ user numbers using an interesting, surname-based model.

The model proved to be rather accurate, it predicted the 10 million users milestone, and the latest numbers indicate that Google+ may have 18 million users at this point.

"The viral growth of Google+ has slowed somewhat over the past few days, but my new-and-improved 1,000 surname model shows that more than 750,000 people joined the site on Monday, bringing the total user base to just under 18 million," Paul Allen wrote on Google+.

"Last week we saw two days where more than 2 million signed up in a single day. If that rate had continued, Google+ would have reached 20 million users by last Sunday night," he said.

This is what led him to predict that Google+ would hit 20 million users by the end of last week. That did not happen as growth slowed down considerably.

"But the last four days have averaged only 948,000 new users and yesterday the site added only 763,000. Yesterday's growth of 4.47% was the slowest viral growth since Google opened up invites back on July 6th," he explained.

There can be several reasons for the slow down, which was to be expected. For one, the initial hype was bound to die down eventually.

Also, the number of people wanting to get in as soon as possible, regardless of what Google+ was like, is dwindling since they've all made it in by now.

Google now has the tougher task of enticing regular users to give Google+ a try and convincing them that joining yet another social network makes sense. Of course, Google has a lot of marketing power which it hasn't been using, all of its sites visited by a billion people each month.