Search giant follows Facebook’s lead, allows users to recommend content and ads with “+1″ button.

Google launched “+1″ today, a feature that allows users to recommend web content and ads to others in a similar manner to Facebook’s Like button. The +1 button will appear alongside search results and website content, and users’ interactions with it may be employed to target future ads and content to them, the company said.

In addition to search results, the button will appear alongside AdWords ads, though the number of recommendations an ad receives will not be used to inform quality score or ad placement.

To make recommendations, users must be signed into a Google account, through which their endorsements will be shared with other users connected with that account. Their Google chat buddies would be one possible example. In a blog post published today, the company said it “may also incorporate other signals, such as your connections on sites like Twitter, to ensure your recommendations are as relevant as possible.”

The first time a user clicks the +1 button they’re given the option whether or not to grant Google permission to use that behavioral information “to personalize content and ads across the web.” To date, Google says it has not used search behavior to target ads across its network, but this introduction represents a step closer to doing so, making use of users’ post-search behavior but not specific search terms.

In a separate post on Google’s AdWords blog, the company suggested the button would also aid advertisers gain more quality traffic. “We expect that personalized annotations will help users know when your ads and organic search results are relevant to them, increasing the chances that they’ll end up on your site… Think of +1 buttons as an enhancement that can help already successful search campaigns perform even better,” the post read.

The feature will be slowly rolled out across Google’s search properties, starting with Google.com. It will also begin appearing alongside other content on other Google properties within weeks, the company said, suggesting integrations with sites such as YouTube are in the works.