"My son's friends don't call him anymore, and now we've become concerned about his social skills."
Michele Novotni, Ph.D.
It sounds like you are very observant and have taken a number of positive steps which could be of help to your son if he were willing to work in this area. Unfortunately if your "help" is not helping, it isn't help. You may need to wait until your son realizes his difficulty before he will be responsive to your feedback and suggestions. Most people strongly desire to be liked by others and be connected. It's a very strong motivator and hopefully will facilitate his desire to grow in the area of social skills and relationships.
In the meantime you could try to support him in the following ways:
You may find it helpful to leave the book, What Does Everybody Else Know That I Don't? (Specialty Press, 1999), in a location in his sight but not as an obvious, direct hint. He may pick it up on his own when you aren't watching.
If he has a difficult time reading, he may also benefit from some of the short, informative articles or answers in ADDitude magazine. These may also be left around in a convenient place.
You may contact his school counselor and ask the school personnel to help keep an eye on his social relationships, especially when he is working in small groups.
It's a good sign that others are still willing to go out with him and that he's not left home alone so he must be doing something right!