Why are "girls" at "my school" doing this?

Okay, some "girls" keep adding my Facebook page. But they are using fake pictures (i've seen them ALL over the internet before, I'm 100 percent sure they are fake) and adding people from our school. What the heck? I mean, what's the point of that? They usually steal pics from girls in bikini pictures or other pictures that show alot of skin and say that they are them XD. Why do you think they are doing this?