When I post a link to this site in Facebook, ithe preview shows a blue square with "xenForo" in it, with the forum title and autelforums.com next to it. Replacing that graphic with something X-Star related would help visibility on FaceBook.
Haven't got to it yet, but the default share image will definitely be changed to one that better suits the forum. UPDATE: Done, we have a new image when being shared on Facebook, Google+, and other.
After trying three types of URLs (homepage, forum and thread), I could not replicate this. All show the new share image (attached a screenshot). Please try entering the URL in Facebook Sharing Debugger. Does it show the image?