I am sure we all have visited numerous forums and photography sites over the years. It is remarkable that even the big sites only have a small core group of really active members. They are the ones commenting and helping with queries. The only difference is of course the amount of members, that post pictures and have queries, after which they vanish. Or the backslapping brigade that only post pictures, waits for comments and not participates in discussions or comments on other peoples pics. I think the latter group are the biggest contributors to photography forums.
I have tried to get many of my students, camera club members, friends and family to enjoy and join CC. The reason they did not, was because to them the site seemed cliquish and they felt like they would intrude. One person said they felt like a stranger interupting a friendly chat between good friends. I know when people join and introduce themselves they get a nice warm welcome from 10-15 people. but you have to get them to introduce themselves in the first place. So what to do......
I do not have any answers, but I would think you let things be and have a site for 25 people or completely revamp the site.
Make the site unique in one way or another. For example, tell people they get serious critique/praise on their pictures when posting. And give them serious critique/praise. Horizon not straight, over exposure, background distracting, lovely B/W conversion, great use of perspective, etc. It will be boring after a while but not for the recipient. And never ever just say "nice capture"!!
Or market the site as a fountain of knowledge for all things photographic. They have a photographic related question this forum will
The site than needs to state clearly its intent and a concerted effort of all active members promoting with facebook and friends should get you a start.
These are just my ideas, do note Mike, pulling the plug was not an option ;-)