I'm scared of my teenage daughters eating habits. How should I take action?

Yeah, being practically anorexic for a boy is never a good thing. I think you should keep trying to bring her to someone for her to talk to. That can greatly help. Other than that, you just need to try to convince her that she's perfect the way she is, and that she doesn't need to lose any weight for anyone. She'll hopefully get that through her head eventually, but in the meantime, you just need to keep showing her that she's beautiful and looks great the way she is.