I sympathise. It is agony to watch.
DS, also autistic, had no friends at that age. Or when he was younger. And he always said he didn't want to go to clubs.But i did make him go to one as he was good at something. He made no friends there, but gradually I realised people were trying to befriend him and he wasn't picking up on the cues.
So I spent a long time teaching him the cues and explaining how friendship works. It isn't instant. You don't immediately connect. It builds very gradually through shared experience.
My advice would be to insist he tries at least two clubs or societies for a whole year. I had to encourage DS to go every single time, But he did enjoy it once he was there. One club for something he's good at or enjoys - coding, game design, music, chess - anything he excels at because people tend to like other people who are good at what they enjoy. And one for fitness - anything at all that he enjoys enough to keep him fit and out of the house. Maybe something with minimal conversation - a not too competitive swim club or cycling club.
Try and find like-minded teens - other high functioning autists or shy kids who won't be cool and bullying. Help him build self confidence - that above all things is transformative. He doesn't have to try and fit in, he has to be at ease with who he really is and spot when others are trying to be friendly.
DS was really painfully unhappy at how lonely he was but - happy ending - he gradually developed social skills and self confidence and now has four different close friendship groups and a really active social life. But I must admit, I put the hours in with him to help him understand how to get to know people and it was a very slow process.