How to find my 19 year old son new friends for online gaming?

Hi

I’m new here and have joined to try and help my 19 year old son. He is at home with me full time as a result of his autism and anxiety. He is very lonely and socially isolated. His only friends are online gaming friends and he has just had a really bad experience where one of his online friends has been really nasty to him and as a result he has lost all of his friends online. Naturally he is devastated. 

My son plays a wide variety of multiplayer games on the Steam platform and he uses a on-line chat platform called Discord.

Does anyone know how my son can safely make / find new online friends?  Anyone else in the same situation?  Just really want to help and support him in finding new friends online and I’m a bit stuck as to what to do to help.  

Many thanks

Ruth