Almost every new generation of car will either get a new forum website, or added forum group. Fun fact, a lot of these are owned by one company. There is also tapatalk which charges money for access.
I believe VW Vortex[0] is (or at least was) the largest forum by number of users. I have a Tacoma and receive dozens of replies on Tacoma World[1], usually within an hour, on posts I've made with questions or comments about the vehicle. I'm sure there are more.