When I was young I remember being a part of a soccer (futball) team and in cub scouts. I'm pretty sure that I got in there because my parents got me in there (how many 5 year olds say I want to join this club or group). They were great oppurtunities for me to learn social skills (immersion).
With almost all of the people I worked with they could easily do almost nothing (and I am not talking about just spending so many hours on facebook (I litteraly mean doing nothing)).
THE MORAL OF THE STORY: BE PROACTIVE WITH YOUR ASPERGERS KID. Sometimes if you bring an experience or something to them then they will like it. They may not, but you will more likely get your child doing something. ALWAYS CONSIDER THEIR INTREST WHEN DOING THIS, AND DON'T FORCE!
What does this include?
religous institution (a great place to at least help your child create a network)
board games (more on that soon)
Taking the initive to go somewhere the child would like