As Google+ ceased being an “invitation-only” network and became open to all, this week it has emerged as the third largest site in the Social Network and Forums category, according to Experian Hitwise US.

Google+ now available to everyoneThe three-month-old social network looks set to take on Facebook as a serious rival in the social networking market.

Opening up access to their social network created a massive spike in Google+’s market share of visits, with a whopping 1269% growth from the week ending 17th September to the week of 24th September 2011. Last week along the site received nearly 15 million US visits.

In the space of a week, Google+ moved up from 54th to 8th place in the list of most visited Social Networking and Forums category sites.

Statistics from Experian Hitwise US reveals how quickly Google+’s audience has moved through the cycle from the “Innovator” and “Early Adopter” phases to the “Early Majority” and “Late Majority”.

Google has said on its official blog that its ‘Hangouts’ feature has been well-received — enabling up to nine users to link up and chat together on video. The feature is due to be available on smartphones equipped with cameras, powered by Google’s own Android software. Support for Apple Inc. devices “is coming soon,” the blog said.

Google has also made its search engine available from within the social network so that users can search from Google+ and get results not just on the social network, but also from the wider internet.