Prometheus did in fact have a cult, but it was a fairly minor one. It's wrong to think that since a figure appears as an important character in folklore he is necessarily an important cult-figure, though--Roman Jupiter, for example, is more or less nonexistent in the corpus of Roman folklore as it exists, unlike other gods like Mars, who is often connected to Roman and Italian folk-story through genealogy. Prometheus was apparently not actually all that important in Greek folklore, and his role as known to us appears to largely be an invention of Hesiod, who greatly expanded Prometheus' importance. Henceforth we find Prometheus of some importance in poetry but really relatively little importance in actual folklore and cult practice. In any case, Prometheus had an altar at the Academy, which he shared with Hephaestus and from which the Promethea torch-race began every year--Prometheus is often associated with Hephaestus in cult ritual, and he was considered the patron of the Ceramicus at Athens. His tomb in Locrian Opus was also the site of a cult, as was an alternate location of his tomb at Argos (I think Sicyon also had an alternate site), although according to Pausanias the Argives denied that Prometheus was the fire-bringer, ascribing that role to Phoroneus, the ancestor of the Pelasgians. According to Pausanias again Prometheus had a mystery cult at Thebes, or rather that Prometheus was the founder of the cult when he entrusted the ritual objects to the Thebans. He also apparently had some sort of cult center at Panopeus, at which a statue of Prometheus or Asclepius was kept in a sundried-brick shrine of some kind.