First off lets not pretend you supervise any IT people, lets say you hand them their paychecks. IT keeps your equipment running they don't need to be barked at or shadowed by you. They are much more efficient at their jobs than you, after all networking is like breathing air for them. Second this sounds more you guys(girls in this case) just want to act like your in charge of someone, so you try to get IT guy to be your gopher, that's not what they are there for. It may not be that he's introverted, there's probably no one who actually tried to get to know him and he sounds much more technically intelligent than the rest of your staff, so treating him like a leper may be encouraging him to distance himself from you and the staff because you have nothing that you each can relate to. This sounds easily within your ability to "fix" if you only took the time to try. Perhaps a quick 2 minute conversation everyday would help start to improve communication. Good luck.