take a page from A-Rod's book

When Andy Roddick was a new pro, he made it a point to visit his website's forum regularly and respond to fans' comments. I think it really helped him gain a huge LOYAL fanbase because it showed that he cared a lot about his fans and that they meant something to him. Since John's just starting out, it's important for him to understand the necessity of a strong fanbase. He's a great looking guy with an awesome personality to back up his killer game. Making himself available (hardly any time commitment necessary) will get the word out and increase the popularity of his website, as well as himself.
Another suggestion is to start a photo gallery. Obviously not in the forum itself, but it'd be nice if there was a cohesive collection of photos of John other than those (of him in Georgia garb) that show up when you google his name.
Market this guy's face, and you'll have a flock of female fans in no time. Market his beast of a serve and even 'macho' guys will be interested. That's what I'd do.