You can still use Google+ / Google Groups to make a few posts here and there. Even thou the engagements from this site is not so great, you will still get some traffic to your offers. I would suggest to set up a small site or use Wix to create a site, and drive the traffic there instead.
I have noticed, most of the Groups and Google+, the people there care to promote or market their own products or services, rather than having an active communication amongst the joined members.
So, best way is to entice them to visit your site, by offering a free download of product, that may be of interest to them. Can be an ebook, video, graphics etc...
Example : If you have a site or product on Dog, then you can offer something like a Dog Training video or ebook. OR some great tips on Dog Caring and Obedience etc... and put a link for them to download from your site. Ensure your site/page where the offer is, loaded with some affiliate products etc...to get the most of out your site/page.
Overall, Google+ / Google Groups can still be your source of traffic, not much but still ok.
Best : use Torrent and usenet / newsgroups for extra mojos.