Joining to make friends or learn something - scouts, footie, drama, computers, skills
Voluntary work - outside, cooking
Jobs for money - carwashing, garden rubbish clearing, pet sitting, dog walking - have to show willing
Finding like minded friends - Facebook, computer games, make their own pizzas
Pack him off alone to help with specific useful job like decorating, garden clearance, for relatives/your friends (to work on social skills, potential cash earning)
He has to organise - eg first bus trip day out with friend, micromanaged
Changed my tune, gently - 'you don't want mummy sorting out your life forever' 'you need to find things you like, not me', 'sometimes we have to make the effort to organise stuff for friends to do', 'just try it, if you don't like it it's up to you but you've got to realise you've turned down an opportunity', 'if I've paid for this you can bloomin' well see it through', 'try earning some cash, that'll make you feel better, the world doesn't owe you a living you know'.
You're supervising everything from a safe distance.
New angle - girls - happy to hang out with withdrawn pleasant boys, computer games, cooking, teach social skills, jolly along. Yobbish school 'friends' are gutted this age that he has female friends, ha.
DCs made it to 14yo eventually and the above happened OK, big changes, phew. Good luck.