Some people who claim they worship Satan may just be doing so to gain attention; others may have other reasons, such as trying to prove how free they are.
But some people do indeed worship Satan instead of God. Occasionally, I've received letters from them, openly rejecting God and stating their hatred of Christ. These aren't atheists; they have no doubt that God exists or that He is holy and pure. But they don't want anything to do with Him, and are convinced instead that Satan alone is worthy of their worship and obedience. They also believe they can harness Satan's power for their own good.
The tragedy is that Satan is a liar, as those who follow him will eventually discover. He also is absolutely evil, as those who serve him will eventually realize. His one goal is to oppose God in every way possible. Jesus' words are true: "He was a murderer from the beginning, not holding to the truth, for there is no truth in him.... He is a liar and the father of lies" (John 8:44).
But listen: Satan is already a defeated foe! Yes, he is still at work, but someday Christ's victory over sin and death and hell will be complete, and Satan will be bound forever. Don't be deceived, but make Christ the center and the foundation of your life. He alone is worthy of your worship, and He alone can be trusted to take you safely to heaven. Have you committed your life to Him?