Hangouts on Air Moves TOTALLY to YouTube!
By mid September 2016, you will not be able to start a HOA via Google+. But you can continue to start them via the YouTube Live Streaming Events area.
You can see the official announcement on this G+ page (for now):
The link that the page takes you to for help is:
Hangout Mastery members Q&A session discussed how to start up your HOAs via the YouTube Interface – member's only content: http://www.mastery.thehangouthelper.com/member-q-and-a-session-2016-08-03/
This is a BIG change. No more SHOAE (Scheduled HOA Events) soon – Sept. 12th, 2016 is the end of that.