In a recent update on YouTube Help stated that Hangouts On Air will move from Google+ to YouTube Live on September 12. Users will be not be able to schedule events on Google+ after September 12 and the events scheduled to take place after this date need to be moved to YouTube Live.
“Hangouts On Air will move from Google+ to YouTube Live on September 12. If you want to schedule new Hangouts On Air you will need to use YouTube Live. Events cannot be scheduled on Google+ after September 12 and you will need to move existing events scheduled to happen after September 12 to YouTube Live.”
To Users will continue to have access to their recorded events on YouTube. Google+ will have the event content available in read-only format in the Activity Log.Google Moving Hangouts On Air To YouTube Live From Google+,