What activities to do with a 16yr old boy (high functioning)

Hi All, Our boy was diagnosed with Autism back in December 23'. We've had 2 years out of school and have an EHCP in place, with tutors attending 3 times a week, now that we're classed as EOTAS.CAMHS support once a fortnight. 

Unfortunately during secondary school our boy had to experience some awful bullying, which has led to trauma, selective mutism, anxiety and depression. 

He is now in a much better place but, will not go out when his peers are off school (evenings, weekends and school holidays). His peers are the main trigger point for his anxiety and sadly it has led to him not seeing anyone else his age. He does talk with some people online but, he prefers it to be people he doesn't know that well. 

That gives a bit of an idea of our boy. We're now at a point where we need to push him to do more but at a very gradual pace. What do you do with late teens to build their confidence in terms of activities? And I'd love to know of how to build some friendships with similar teens. We really don't want him to fear his peers anymore but, even one friends / someone he can trust would help.