This answer concerns a group that very definitely believed in the demons of Christian mythology, but did not worship them as such. They were however very important to the development of the modern concept of Satanism.

In the late medieval period in Europe, the magical art of necromancy (or “nigromancy” - black magic) was practised. Necromancy involved using magical rituals to summon demons, and bind them to the will of the “master” through invocations. These invocations often called upon the name of God or Christ to give them the authority to compel the demons into servitude. Sometimes specific, named demons would be called upon, using names now associated with the devil such as Beelzebub and Baal. These practitioners were typically educated men, most often clerics or courtiers. They were not demon-worshipers, but they did explicitly invoke demons. They also were not "cultists". Practicing necromancy was really just a matter of getting your hands on a manual and carefully following the instructions within.

Richard Kieckhefer, in his commentary on the 'Munich Manual of Demonic Magic', describes how necromancy was perceived by contemporaries:

“It would be a mistake to think of necromancy as a peripheral phenomenon in late medieval society and culture. Secular as well as ecclesiastical courts took it seriously and at times executed those charged with its practice; monarchs and popes as well as commoners lived in fear of becoming its victims. This fear may have been in some cases or to some degree feigned or pathological, but it was also grounded in realistic awareness that necromancy was in fact being practised, and in an almost universally shared conviction that it could work.”

While the rituals were often inspired by Islamic, Jewish, Byzantine, or even Classical magical traditions, they were written within a distinctly Christian framework. The supposed effects of these rituals (often called “experiments”) ranged from the playfully benign (summoning a spectral boat rowed by demonic sailors that would transport the “master” to any place he wished) to the outright malicious (causing the victim of the spell to suffer from dementia).

Kieckhefer argues that the phenomenon of necromancy had a significant effect on the evolution of the popular concept of demonic magic:

“It was surely in large part because they were aware of the demonic magic described in these manuals and evidently practiced in their midst that orthodox authorities often became skeptical about the notion of non-demonic, natural magic. … In so far as necromancers contributed to the plausibility of claims about witches, they bear indirect responsibility for the rise of the European witch trials in the fifteenth and following centuries.”

It was during the period of the witch trials that the modern notion of Satanism began to take shape. I'm not especially informed about the witch trials however, so maybe somebody else could provide some insight into how the idea developed from there to the modern day. If there's any aspect of medieval necromancy you'd like to know more about, I'll try by best to help.

The short answer to your question is, no. There is no real, historically, verifiable evidence of even any small-scale devil worship. With regards to the "Witch's Sabbath" (the ceremony by witches worship the Devil, often mimicking or mirroring that of a Christian mass), there is no evidence that this ever really occurred (if we're using this a quantifiable example of Devil worship). See Scott Hendrix "The Pursuit of Witches and the Sexual Discourse of Sabbat."

A longer answer would be to follow up on u/neon_dt, with the changing emphasis on how witchcraft was viewed. Prior to the European witch-hunts of the 15th-18th centuries, witchcraft was viewed as an involuntary phenomenon. That is, the witch was either tricked or inadvertently began practicing magic. That is, the witch was perceived as a more sympathetic character, with his plight more attributed to his own ignorance and/or the trickery of the Devil.

This changed with a dramatic shift in the 14-15th centuries (which obviously coincided with the development of the witch-hunts) with regards to how Satan was thought of with regards to both witchcraft and the world. Witches were now seen as active participants in their own calamity. Rather than being tricked by Satan into becoming magical, these 15th century witches were thought to have actively sought out a covenant with the Devil, often times worshiping him in ceremonies (like the witch's Sabbath) and selling him their soul, in exchange for magic.

This active form of witchcraft put the Devil firmly in the center, making it much more terrifying and pernicious than it had been earlier. Thus the idea of Devil worship, and its more modern day fears in the 80s can be possibly linked to these origins.