What religion worships Baal?

Answer 1

Today? None. This form of idolatry is defunct, just like the gods of the Greeks, Romans and Druids, as predicted by Isaiah (2:18). In ancient times, baal-worship was found in the Levant.

And among the Israelites?

Throughout the period of the Judges and Kings, there were individuals who permitted themselves the aberration of dabbling in the idolatry of the neighboring countries, including the worship of the various baalim, with local their local variations (Baal, baal-peor, baal zebub, baal beq, baal berith, baal me'on, baal gad, baal hermon, baal peratzim, etc.).

More specifically, it was Jezebel, the wife of Ahab, who introduced larger-scale baal-worship into the land of the Ten Tribes (Israel; as opposed to Judah). This deviation was soon stamped out by Elijah (1 Kings ch.18).

Answer 2

Baal was a West Semitic god worshipped by the Phoenicians, Canaanites, Israelites and neighbouring peoples, but less so by the people of Judah. The Old Testament portrays Baal worship in Israel as sporadic, under the influence of foreign powers, but Archaeology shows that the Israelites were at all times polytheistic until the destruction of Israel in 722 BCE.