Why does my friend add creepy people on Facebook, Twitter, and BBM?

[Future Apple Employee ]

For instance, last year this one strange person was texting her and sending her BBM messages, and she would complain about him being so creepy, so I told her to stop responding. Well, guess what she does? Continues to text/BBM message him for months! Heck, she might still text him, and it started about a year ago. She also BBM messages these people who say they're from India, Brazil, and Turkey (all males), and the one tried to act like they were a couple. I asked her why she continues to message them, and she replied with an, "I don't know," smiling. She even told these weirdos where she lives and what school she goes to. Most of them ask her for her Twitter username, and she tells them and follows them back.

I also saw on Facebook she's friends with this one man from Indiana (she is the only mutual friend I have with him) who is twenty years older than her, and he has "liked" and commented on a few of her statuses. Some of these creeps also post comments on her photos saying, "Beautiful!" etc. However, she invites this behaviour with her seemingly innocuous Twitter posts such as, "I was having a great day until I saw it was national boyfriend day. Who wants to be my boyfriend?" and, "Boyfriend, where are you?" She's not in a relationship right now, nor has she been for as long as I've known her, so perhaps she feels lonely. But that's no excuse for adding obvious Internet predators! I feel like they're going to stalk her, and it worries me, but I don't know how I can nicely tell her that her actions are imbecilic. It would be understandable if she were, say, thirteen, but she's not—she's seventeen. One of my other friends brought it up, but she just shrugged it off believing these people are harmless (she's kind of naïve). I don't want to do anything about it until I understand why she does it, though, which is why I'm asking this to you all. Please help me! Thank you!