I use Google+ and also facebook for mostly different reasons. I use facebook primarily as a means to share stuff with people I know in real life whereas I use Google+ for discussions with people all over the world on topics I am interested in. I don't think Google+ is in any way a ghost town. I have thousands more people in my circles than I have friends on Facebook and there is plenty of activity. If you aren't seeing activity on Google+ then you just haven't circled/followed the right people, joined the right communities, etc.