Players can't start threads
Per the FAQ
There are four levels of access in a game:
Player: A Player is just a normal player in the game. Players can reply to threads and send private messages. They can read messages in any group to which they are assigned. They cannot start new threads.
Moderator: A Moderator is a player with a few extra privileges. Moderators can edit other players' posts, in the case of misbehaving players. Moderators cannot see Private Lines or Private Messages which have not been sent directly to them. They cannot start new threads, and they cannot see whether rolls on the die roller have been fudged by the GM.
GM: GMs, or Game Masters, can add and edit players and characters in the game, and they can see all posts (regardless of group), and all Private Lines and Private Messages, whether they are addressed to them or not. GMs can do anything the Game Owner can do except edit other GMs (that is, they cannot edit other GMs' characters, access, or posts). The Game Owner is the GM to whom the game is registered -- only they can edit other GMs. All GMs can start new threads, they can edit and delete players' posts, and they can see whether die rolls have been fudged.
NPC: NPC stands for "Non-player Character". For all purposes, their access is just like that of a player. This is usually used by GMs to denote characters who are played by them, rather than by players.