One notable creepypasta that involves a devil-worshiping cult is "The Rake." While it primarily focuses on a creature known as The Rake, some variations of the story incorporate themes of cults and ritualistic practices related to devil worship.
Another creepypasta worth mentioning is "SCP-001: The Gate Guardian," which, while not directly about a cult, includes themes of worship and entities that draw a cult-like following due to their otherworldly nature.
Additionally, "The Cabin in the Woods" isn't a creepypasta but features a similar premise where a cult-like group sacrifices individuals to appease ancient gods, blending horror with cult themes.
If you're looking for more specific cult-related stories, browsing through various creepypasta websites or forums could yield many user-generated stories featuring such themes.