Last December, we introduced +Post ads to a limited number of advertisers as a new way to amplify content and create conversations across the web. +Post ads let you to take a piece of your public Google+ content, like a photo or video, and turn it into an engagement ad that runs across the Google Display Network.
Starting today, +Post ads are available to all advertisers who meet a minimum threshold of Google+ followers. We’re also piloting two new features - promoted Hangouts on Air and automatic post promotion - to help you create compelling ad experiences and make it easier to extend the reach of your social content. Google Releases +Post Ads In AdWords, And Tests Hangouts on Air [adwords.blogspot.com]
You can now promote your Hangout on Air with +Post ads that lets users take specific actions before, during, and after the broadcast. Users can RSVP prior to the Hangout, watch the broadcast live, and view a recording after the event.