It is a result of an overall lack of education.
Parents don't want to talk to their kids about sex for any number of reasons (it makes them uncomfortable, it is a taboo subject, it goes against their beliefs, or they fear that talking about it will make them curious and want to have sex).
Parents don't want the schools to teach their kids about sex, so kids are left to learn from their peers or TV (or even the music they listen to).
I am not blaming TV/media, but parents need to be aware of what their children are hearing and seeing on TV and talk to them about it. If a parent doesn't want to take the time to have a tough conversation and educate their child or monitor what they are watching or listening to, they shouldn't be surprised when their kid gets and STD or gets knocked up.