There are different forms of Satanism.
As others have pointed out, the kind that is embraced by the so-called "Church of Satan" is decidedly non-theistic, a hedonistic philosophy that caters to the taste of rebellious youths in their "misunderstood genius"-phase. They don't worship Satan as a literal being, but use the imagery to contrast their own POV with what they perceive to be the evil of Christianity: oppression of the individual, oppression of natural urges and so on and so forth. It's more than a bit straw-manny, but that's how it is.
There are theistic Satanists as well, though. One example would be the Temple of Set, which splintered off of the CoS in the 1970s, if memory serves.
They are theists who've moved beyond the unhealthy focus on Christianity, and worship the deity of radical individualism in what they believe to be its oldest known inception: in the form of Set, the Egyptian deity of the desert, storms, and darkness.
They conceive of him as a positive figure, a challenger of stagnant order, a breaker of misconceptions, kinda like Prometheus the Titan, who stole fire from the gods in order to give it to Man, thus destroying the status quo.
Their relationship with their deity is not so much centred around submitting and obeying, but more like a teacher-pupil-bond.
And in the end, there are stupid teenagers at the fringes of the "goth"-culture, who just want to be crass and flashy, but usually don't know what they're doing.
