Advice needed :)

I don't quite know how to start really. I have been in a relationship now with a girl for 6 months and she has an autistic son who is now an adult. Her son suddenly left home without warning and set himself up in a flat and has had no contact with his family for over 4 weeks now. Obviously this has left the mother distraught, confused and very lost as to what is going on. My girlfriend has told me that she believes she is also autistic and with her son leaving suddenly it has left a huge hole in her life. I'm trying to deal with a number of things at the moment but my main priority is to my girlfriend who i am trying to support and help. I'm just wondering what her next steps should be in regaining communication with her son. Thanks for listening and any advice would be very grateful.