I think the game Spyfall would work well as a forum game. It is a social deduction game where players are either trying to find the spy while at the same time not letting the spy know their current location. The randomly determined spy will be trying to figure out the location without revealing that they have no idea what it is.
The players take turns asking each other questions to attempt to find the spy and demonstrate their own innocence.
Spyfall | Board Game | BoardGameGeek
I'd like to get 5-8 players if I can. It doesn't really go well for the spy with 3 or 4. Anyone interested in trying it out?