Vienna -
Visit a provincial mental health facility , and have them file your information regarding the young man .
Ask them what can be done to help your friend - he needs professional help,
Provincial staff are caring and trained with every resources for assesment and treatment which he needs desperately (and maybe wanting, but as a cult member is afraid to stir the dragon)
I suggest this route over law enforcement (prosecution), or Humane Societies whose agendas are often co-opted towards publicity rather than help.
Please do this right away as much is already at stake for both your young lives ....