Should I start talking to this guy more or move on? I only talk to him every few weeks...?

I think he might be interested and he sounds like a good guy, just a bit weak in the being-sociable sector. I think you should add him on Facebook/MSN and start talking to him there, plan a lunch date, and get to know him :) I think, because he's shy, he'll open up a bit more like this. Good luck!