Teen artists will usually have the following things in common for target mass appeal:
The majority of their songs will be about love, relationships, breaking up and other similar topics in order to attract a loyal following by the opposite sex.
Since its the band as a whole which is being carefully marketed as a complete package, the record label is very careful not to let any one band member outshine another. Everyone is kept on a very short leash. This explains the matching outfits the band wears during press photos.
Although a whole package, each band member will all take on different character for mass market appeal so as not to alienate any demographic. For example, every band will have the "strong but silent type" the "friendly heartthrob" or the "slightly goofy but appealing joker".
Since most fans will wish to start a relationship (or just have sex) with the members of the band, the band will be extremely friendly to all their fans letting them think that they can. This is especially true if the fans are loyal enough to buy all the band’s merchandise.
Girl artists usually are marketed as both sex objects to appeal to men and boys and the wholesome neighbor next door to appeal to their female fans. This is why you often will see someone like Britney Spears dress provocatively showing off her breast implants, while at the same time attempting to maintain her wholesome innocent image. It’s a tricky balance but one which when pulled off usually equates to high financial rewards.