I'm working on an Open Source video game engine https://github.com/samgj/mlnmone. I was wondering if there are forums provided for GitHub projects because, I need communication with any potential volunteers. I would also be fine if there were other forum hosting sites that I could use.

Github has their issue system which you can use as a sort of forum, as well as a wiki.

It is hard to start a forum because no one want to be the first poster in a forum that is empty. Guestbooks are the opposite where people leave a note just to say hi when it is empty and keep important information if they see a full page.

There's a useful comparison at http://en.wikipedia.org/wiki/Comparison_of_open-source_software_hosting_facilities - there are several hosting sites that offer Forum functionality (e.g., Sourceforge) (even if you're hosting your code elsewhere, you can still make use of just some of the functionality, such as Forums).