There is a site, similar to PostLoop called TheForumWheel, which will pay you to post threads and replies to threads in third-party forums.
For content creators: You can sign up at the Forum Wheel, but you must post 10 grammatically-sound, well-formed posts in their "Gateway" forum before you can start posting in third-party forums and earning money.
Each post you make on a third party forum is worth 1 credit ($.05). You can withdraw your funds at any time via Paypal. You can also enter competitions to win a jackpot prize by spending the credits you earn on tickets in the prize draw ( although this is not often used by creators).
For forum owners: You can sign up and buy a set amount of credits which can be used to pay content creators for their threads or replies.
There are fewer forums currently available on TFW than are available on Postloop, but they always seem to be in credit, and there is one forum on TFW that pays twice, once from TFW and once from the forum itself!