Is HE unhappy with his life? Or are YOU unhappy with it?
If HE wants to change, then you can help him do that by encouraging activities that will help him broaden his circle of acquaintances and increase his self confidence.
This could be anything from educational opportunities to physical activities or volunteer work. Any one of those will help him learn to interact with others more; at least, if that's what HE wants to do.
If YOU are the one who wants this FOR him, then none of it will work.
As long as your son is happy with himself and his current life choices, your job is to love and accept him just the way he is. No change necessary.