Is Bill Kaulitz a Satanist

It's true he doesn't believe in any religion but he does believe in spirits and that life doesn't just end. You can find the interview on the official US forum.

He doesn't believe in any religion.

NO! He's too nice for that

Also, Bill says that he doesn't not have a religion at this time. But he believes in God, so he can't be a satanist. If you think it is because of how he dresses, then you are getting a wrong impression. That is just Bill's style.