Only admin and mods can close threads. You will have to request that they be locked and once locked, only mods and admin may post in them. No one else.
Oh, okay... was hoping there might be an option to keep it just to the players... I've been on one or two sites where they don't have that option and a spammer will come in and post right in the middle of the roleplay.
*nods* If that happens and it isn't found prior by staff and thus deleted, please report it and we will delete it for you and take care of it should we need to on top of things.