Just want to second the yahoo groups suggestion. The one listed in 4evermom's post is a great link. Within the HSA there are chapters for Burien, Enumclaw, Federal Way, Issaquah, Kent, Renton, Pierce County, and a Teen Group.
For those of you that have not heard back from yahoo groups, please try again. I know that there was a merge over the summer of several smaller groups and a restart of the Issaquah group.
I am new to HS'ing and started going to park days this summer with the intention of finding some companions for my 7.5yo son. One thing I learned is that the same people don't always show up so it is worth it to keep going again and again until your schedules sync with someone that might be a good companion. We have been to about 10 park days and are slowly finding kids that my son clicks with, so it isn't always a quick process.
I know what the feeling is like when your kiddo's don't have any close friends, I was laying in bed with my son chatting before he went to sleep tonight and feeling huge guilt about him not going back to school next week because once again I feel like I've yanked out from under him the base he had for starting friendships. We had toddler group friends that we stopped seeing once he went to preschool, then we stopped seeing the preschool friends once he went to kindergarten, we switched schools for him in 1st grade and made some new "friends" and then I decided to HS so now those friends are gone. He has had lots of "friends" over the past 5 years and none of them have really stuck, we move on and then other people get busy too. So I don't know if that is any better than finding 1 or 2 friends that HS that can be there for the long haul.