Many are familiar at this point, so I tried Twitter, because I'd heard of it and wanted to know more about it. Twice I tried to open an account and couldn't get it to actually say I have been accepted. It was taking a time out to work with stuff, so maybe that's why. I'll go back later.
Craigslist is extensive. There are many uses for it, not sure if the library would want to use it for anything. I remember a woman from Minnesota or Wisconsin venting about library patrons on Craigslist. That would not be advised.