Not sure if all this can be really useful as I have never been hosting a mafia game and I'm pretty new in the game, but here are a few things which came to my mind when working on this:

The person organising the game gets in the Game Master (or any other similar name) Group. He has moderation rights on all forums and on group moderation.
He post the rules in the public section so that anyone can find them fast if needed.
Day and Night Phase thread can stay on TOG or here. Either way.
Before starting a game, GM sets all groups to HIDDEN so that no one can see who is in each group anymore except for him. No more group colour nor group name on index from that moment.
He puts the guys who can know from the start each other (like the mafia) in their respective group and post an intro for that group in their specific private forum only viewable by Mafia Group and Game Master.
Later in the game, he can put ppl who found each other like teh aliens ie. in their own hidden group and forum also to facilitate discussion, help and moderation. Rest stays with use of PM as before.
When game is over, he sets all groups to closed and if he wants to, open all discussion threads to forum members so that everyone can have fun reading the plots that has been going in their back during the game.