First of all, I am a guy.
I have friends who have been raped. So I wondered about it and now I have some questions. How would a girl be able to tell that a guy might rape? Any red flags that they should know about? When they are in trouble what could they do to escape? While being forced, how could they fight back? I know this is gross but...during sexual positions? If we can figure this out, a lot of girls might be spared serious trauma.
Last, the most common reason I have heard that they don't want to report it is that they don't want their parents to find out. Shouldn't there be legislation to help teenager girls to get justice where it is due without their parents finding out? It is a big discouragement and the law fails in its primal quest to protect the innocent.
All of your questions are good and valid. The most important thing to understand about rape is that it is about power, not about sex.
Though rapists don't come in one shape or size, it is hard to generalize about a type, but a commonality is dominance, power, control, etc... And actually the reason most women don't report it is that they often know the man who raped them and they don't want to get them in trouble and they don't want to set themselves up for ridicule, which often happens. As for what to do, there are some great self empowerment classes -- which differs from self-defense in that it teaches them not only about how to fend someone off, but how not to get into that situation in the first place. I think that's all of your questions -- try RAINN for more information.