Afraid I'm guilty of the 'social media' thing and so here less often.
There are a number of specialised Facebook groups which, while many are set up as a selling platform by the administrator, do get a reasonable amount of traffic. I frequent a specialist group for Charles I coinage and several for hammered and early milled because that's where my interests lie. Probably of little interest to the many(?) penny enthusiasts here, but I've certainly contributed to the Charles I group quite frequently and it's where quite a few of my Charles I contacts congregate..
There are also groups for numismatic literature and historical medals, which again though specialised fall within my interests and a few detectorist groups where I try to identify items. I also admit that I frequent many of these groups to spot potential purchases since there are a number of well known dealers who are also members there. Some, like Tim Medhurst rely heavily on social media (he's primarily on Instagram I believe) and it's not uncommon for things to never reach a dealer's website, having found a buyer on a Facebook group.
I'm not saying that's an ideal situation, it's all too easy to miss something because you don't happen to be a member of a particular group, but I accept that's the way of it (even Spink sell stuff on Facebook now). Plus I'm chronically online anyway, so it's just a few more pages to visit in a day. And if it results in a bit more knowledge, whether a collector ticket identified or a potential contact spotted, a possible new source of material or an item added to the collection, all to the good.