I was a member of Purestorm around 6-8 years ago then had a break for a while due to an issue with mods (happily resolved). Since rejoining I have noticed the number of people online has dropped by at least a third. I often used the online feature to find models to replace "no shows" or for last minute bookings but now I never see more than 2 lines of text in the "Who's Online" section of the Forum page.
Is this down to more accurate web function, less people shooting or have people moved to other sites?
My personal experience is that Facebook (and to some extent Twitter) is now a much greater force in securing shoots than it was even a few years ago. There are groups, both regional and national, geared towards finding models - last minute or otherwise - and of course the notifications go direct to peoples' phones. Nine out of ten of my shoots are arranged there - the other one here. FB works well if you're an established photographer with a track record on a recognised modelling site such as Purestorm but perhaps less well if you're new, or thought to be new, to model photography. Or if you're primarily interested in working with local models FB works well too.