A few random thoughts about ghost town. Is G+ a ghost town? It actually depends on whether you use it or not.
There's a whole bunch of people that created G+ accounts back in summer 2011, added each other to their circles, posted the obligatory "I'm here" and went back to their main social network at that time. Every once in a while, as G+ adds new features, some of those people "come back", take a look around and declare it to still be a ghost town. And they are quite right. It's not that they're using G+ wrong. It's just that they're not using it at all.
You can do the same for any social network. If you take this nebulous blob of people you follow (with some of them following you), and they all register new accounts on another network, but then go back to "socializing" where they (and you) were before, of course the new one will forever be a ghost town for you - unless you find new people to follow. There are at least two barriers to the migration - you don't want to "lose" the content in your stream (people you follow), and you don't want to "lose" your follower count.
So that big cluster of people stays where it was two and a half years ago, growing their followers and having conversations using whatever tools that specific social network provides.
And some people even go as far as doing fortnightly drive-by binges, where they do a bunch of link posts, one for each one of their latest blog posts. They never reply to comments on those posts, they never +1 or reshare other posts, they never post links to somebody else's content and they never comment on other people's posts. Needless to say, if you want engagement, you need to engage. Constantly. Otherwise, it will still look like a ghost town to you.
So there's that small part of G+ which is indeed a ghost town. A tightly connected and rather small (in low hundreds) graph of people who never got to experience what this place has to offer. And there's a much bigger part of G+ that is a very vibrant and a very diverse planet. You get to pick and choose which tools you use and how you use them.
You can be here by just having a Google account. Or you can be here by actually being here. Interacting, creating, finding new things. Find a new tribe (or two) to be a part of. And never look back until you find something better.