Google first introduced social search on google.com in 2009, allowing users who are logged into their Google account to be served search results based on recommendations from connections within their Google Social Circle and other networks such as Twitter and Facebook.
Social search results are mixed through a user's results based on their relevance, with annotations below the results and a picture of the connection who may have recommended the link.
Yohann Coppel, software engineer at Google, said: "In 2009 we first introduced it on google.com as an experimental feature designed to help you find more relevant information from your friends and the people you care about. Since then we’ve been making steady improvements to connect you with more people and more relevant web results."
The roll-out follows last week's spat between Facebook and Google, when it emerged the social networking site had hired PR agency Burston-Marsteller to spread negative stories about Google.
Facebook claims it did not approve of the inclusion of Facebook data in Google’s Social Circles, and pointed out that users should be aware of how it was being collected.
Earlier this week, Bing, which powers search on Facebook, announced it was deepening its relationship with the social network to include data from its "like" button to make its search function more social.
In March this year, Google added to its social features, with the introduction of the "+1" recommendation button to rival Facebook’s "like".