It depends on who you ask. 'Because' is not in the same syntactic category as 'and', as they show different behaviour:
(1) a. I am looking for her because she is missing.
b. She is missing and her boyfriend is dead.
(2) a. Because she is missing, I am looking for her.
b. *And her boyfriend is dead, she is missing.
More traditional approaches categorise 'because' as a subordinating conjunction in the same category as since, as, if, as long as, although, etc., as opposed to coordinating conjunctions like and, or and but. More modern approaches subsume the category of subordinating conjunctions under prepositions instead. A prominent grammar that advocates the preposition view is the Huddleston and Pullum grammar. Pullum also makes the cause that because is a preposition here. The basic idea is that a preposition may subcategorise for a full clause, which is what 'because' can do.