D'varim (Deuteronomy)13:9(8)
Lo-toveh lo velo tishma elav velo-tachos eynecha alav velo-tachmol velo-techaseh alav.
Do not agree with him, and do not listen to him. Do not let your eyes pity him, do not show him any mercy, and do not try to cover up for him

In the name of our Lord Yeshua the Messiah, you being gathered together, and my spirit, with the power of our Lord Yeshua the Messiah, are to deliver such a one to HaSatan for the destruction of the flesh, that the spirit may be saved in the day of the Lord Yeshua. (1 Corinthians 5:4-5)

1 Corinthians 5:11 But as it is, I wrote to you not to associate with anyone who is called a brother who is a sexual sinner, or covetous, or an idolater, or a slanderer, or a drunkard, or an extortioner. Don't even eat with such a person.

Whoever transgresses and doesn't remain in the teaching of Messiah, doesn't have God. He who remains in the teaching, the same has both the Father and the Son. If anyone comes to you, and doesn't bring this teaching, don't receive him into your house, and don't welcome him, for he who welcomes him participates in his evil works. (2 John 1:9-11)

These are people who claim to be believers, but in truth are leading others to idolatry. We are to have nothing to do with them. The traditional view says that we are not allowed to have pity on a Maysit, a misleader to idols, nor is he allowed to help him in times of need, even if his life is in danger.

Perhaps this is going too far. Although we are to avoid such people, and treat such a person as an enemy, the Torah does say that we are to help our enemies as well.

Shemot (Exodus) 23:4-5 If you meet your enemy's ox or his donkey going astray, you shall surely bring it back to him again. If you see the donkey of him who hates you fallen down under his burden, don't leave him, you shall surely help him with it.

Perhaps by doing so, you can draw him back to the truth.