I've been in a local club for about 5 years, it's existed almost 60 years. The membership has always fluctuated, we've more than doubled since I joined and we've had to move meetings to a new location. We are very informal, but with a small yearly fee to pay for room booking, projector, nibbles, etc. Most of the members do participate in the monthly friendly slideshows, but it is usually a smaller core that does the organizing. We're a 'self-serve' club, if someone wants a speaker or a workshop it probably won't happen unless they organize it
(more experienced members will guide though).
We do have a website, facebook page, flickr group, etc. The online participation isn't really huge given the size of our group, but they do work for notices and I suppose advertising. There just isn't a good platform that people will universally use for online discussions. Facebook is the most used in our group but honestly I think it's horrid for any sort of discussion or image sharing. I can't handle its ephemeral nature.
There are a couple of 'Facebook only' photo groups near me, but they're largely the 'pat on the back' image sharing type (not that this is always a bad thing). I really, really hope these don't push face-to-face clubs to the fringe.