If you have seen them with proper clothing and make-up in proper movies, most of them would not have much, if anything, to make them less attractive than regular movie/pop stars. The packaging context and presentation matters, and having them sing/play roles in Hollywood movies, creates all kinds of secondary attractiveness factors related to the content and presentation (as opposed to the merits of the person).

The opposite is also true. There are teens who believe e.g. that Jennifer Lawrence is a crazily attractive girl, whereas one could argue there are several just as, or even prettier, ones, in their high school. It's the added myth, styling, and exposure that's shoved in their minds that elevates her. (And similarly for male actors). Of course there's the occasional Errol Flynn or Brad Pitt, or Ingrid Bergman or Margot Robbie - but most of them are elevated ordinary people + Hollywood allure.