This is a question not easily answered since every Pagan has his or her own opinion on the subject.
Most Pagans will agree that whatever else Satan maybe, he is at least a Deity of the Judeo-Christian-Muslim pantheon.
Because Satan is specifically a Judeo-Christian-Muslim Deity.
Since many pagans choose to retain no connection to the Judeo-Christian-Muslim pantheon unless they consider themselves Christopagans or Judeopagans, most Pagans do not believe in Satan or give him any energy or homage.
Since most Pagans do not believe in Satan, they do not worship him.
Pagans don’t necessarily describe their relationship with Deity as one of worship, so the idea of worshipping Satan is a foreign concept for many Pagans in any case.
Do Pagans believe Satan exists or not?
Again, a Pagan’s point of view is going to reflect his or her view of Deity in general and will derive from where he or she puts him or herself on the God Map.
Remember that, as it is used by many pagans, the term Deity can refer to any supernatural or spiritual being, force, or power.
Therefore, Pagans generally consider Satan a Deity.
If a Pagan believes that Deities are anthropomorphic beings, for example, then he or she will view satan as an anthropomorphic being.
If a Pagan believes that Deities are archetypes, then he or she will view Satan as a psychological or energetic pattern.
If a Pagan believes that Deities are currents of power, then he or she will probably view Satan as one or more specific energy currents.
If a Pagan views Deity as a thought form, then he or she will likely take the position that even if satan didn’t exist before, he does now because of all the energy that millions of minds have fed into him over the centuries.