All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
We have already issued Fataawa 81150, 88957 and 87952 on the ruling of masturbation, so please refer to them. You should advise your brother and teach him that masturbation is forbidden as has many disadvantages on his health and his personality. Besides, you should find good company for him who will help him and urge him to do good. Among the things which would help your brother to avoid masturbating is avoiding places and scenes that incite one's desires.
Allaah Knows best.