좋아하다 means to like , 좋아해요 (해요) is informal polite speech , 좋아합니다 ( 합니다 ) is formal speech, if you want to ask someone whether he/she likes them or not you can say BTS를 (방탄소년단 을) 좋아하니까? and it's a formal way to ask but if you're speaking with a friend or someone close you can drop the 을/를 ( when you are speaking only! ) if you are going to write it you should put the object particals you can say BTS 좋아? or BTS 좋아해요?
좋아하세요 too can be used to ask someone
the only difference between 좋아하세요 and 좋아해요 that 좋아해요 can be used to talk about yourself too 제가 방탄소년단을 좋아해요. ( I like bts )