I think you're barking up the wrong utility pole if you truly believe that there are actually any genuine "devil worshippers" out there (outside of perhaps a few psychotics who should get professional treatment). That's a misunderstanding foisted upon us by the ardent Christians with Medieval mind-sets.
Those who say their religion is Wiccan (witches) do not worship the Devil. The adherents of the so-called "pagan" religions do not worship the Devil. The ancient Druidic religion was not "devil worship." It's important to remember that in this theistic mythology the Devil is in no sense the direct opposite of God, with the two somehow locked in eternal struggle. In this belief system, God is one and absolute, omnipotent and omniscient. The Devil is just a renegade angel, the direct opposite of the Archangel Michael, not of God.
If you're interested in devil worship, I suggest you're on the wrong site in the wrong century and with wrong pre-conceptions. You could, of course, try Googling it. There are probably scammers out there who'll tell you just what you want to hear.