It isn't really that noticable on the forum, but if you look at the top of the page where it says "Logout" and your username, you'll see a little orange speech bubble three icons across to the left which leads you to the main chat joining page (I've posted link below for convenience).
Just need to click on the big button saying "Open pop-up chatroom" and sign in as your forum username. Simple as that.
Considering this has come up... I do wonder if it's worth trying to do a sort of regular chat "party" thing every Saturday or something to all socialise and get it in use. Depends how many are interested, what day is best and what time would be best.