Pray for him. I would tell him straight up that what he is doing is wrong and it will lead him straight to hell. That no amount of fame or money is worth going to hell for. Here is some of what Scripture reveals about Satan:
1) Satan has power enough to oppose even the angels (Jude 9; Daniel 10:12-13).
2) Satan seeks to deceive by masquerading as an angel of light (2 Corinthians 11:14-15).
3) God has provided the means of defending ourselves against Satan’s attacks (Ephesians 6:11-12).
4) Satan’s power is limited by God’s will (Job 1:10-12; 1 Corinthians 10:13).
5) As “the god of this world,” Satan has dominion over those who live without Christ in the world (2 Corinthians 4:4).
Surely, there are those who suffer under direct satanic control, such as the young medium of Philippi (Acts 16:16-19). And there are those who have devoted themselves to the devil’s work, such as the sorcerers Simon (Acts 8:9-11) and Elymas (Acts 13:8). However, in each of these three examples, the power of God prevails over Satan’s slavery. In fact, Simon is offered a chance to repent (Acts 8:22). Obviously, there had been no irrevocable “selling” of Simon’s soul.
Without Christ, we are all under condemnation of death (Romans 3:23). Before we are saved, we are all in bondage to the devil, as 1 John 5:19 says, “The whole world lies in the power of the evil one.” Praise the Lord, we have a new Master, One who can break the chains of any sin and set us free (1 Corinthians 6:9-11; Mark 5:1-15).