This is not Google+ directly, so I'm not sure if the answer for Google+ is relevant.
I've had a great time working with you all in the Webmaster Central forum, but it's time for a small change. As the Google+ platform grows and the +1 button social plugin becomes a more integral part of that Google+ platform, we'll be moving the primary support channel for questions about the +1 button on your site to the general Google+ platform forum.
From Webmaster Central on Google Product Forums, filtered for “Google +1 button” category.
So in my opinion, you can either use these forums or the Send feedback form from Google+ pages.