Another poster suggested medications. When I did my mental health clinicals, I learned medicine just masks social anxiety disorder and lots of times it is a behavioral issue with children (not saying it is behavior he is choosing to do and he may not even realize it). There are many, many ways that he can slowly be introduced into group settings until he is comfortable. Kind of a desensitization like allergy shots. I would suggest behavior modification techniques at first - kids are so sensitive to the anxiolytics/antidepressants/antipsychotics and their risks often are far worse than the mild benefit they might get. Medications always need used with therapy as there is almost never just a chemical cause to something like this. Good luck, it can get better and be managed with the right person helping you.