Can't find (nor remember) the VFTT threads Sanbu is talking about, so I'll answer Mike P's variation of the question.
Looks like RocksOnTop is no longer in business.
I seem to recall both the AMC and the Mt Washington Observatory had pretty active forums once upon a time. Can't find them now, but WhiteBlaze.net is still running.
There are a few sites aimed at technical climbers, that include trip reports, conditions, etc. - MountainProject.com, NEIce.com. Ditto for skiers - e.g. timefortuckerman.org
Summitpost.org is still running. The encyclopedia aspect is still useful, but the trip reports are becoming infrequent and the forums are practically silent.
There are lots of meetup groups for hiking and climbing - some are more organized than others. Most are not particularly useful for Q&A nor designed for sharing reports and conditions.
The pre-Internet clubs remain active - you'll run into big groups out on the trail once in a while. AMC, ADK, MIT Outdoors Club, Dartmouth Outing Club... Some have online forums for members.
Couldn't tell you about Facebook. I have an account for business reasons, but I don't use it for anything else. From my experience with Facebook, though, it's probably not easy to search for anything.
I know of some active fora aimed at other regions (e.g., Pacific Northwest) but I assume the threads Sanbu was asking about were focused on the Northeast.