Personally, I think perception has a lot to do with this.
Take false accusations of rape, for example. There is a very small chance of this ever happening. But because cases are highlighted in the media, a lot of boys (and men) think it's fairly common place.
Males seem to be in a constant state of disgruntlement over what they consider 'grey areas'. However, because the perception is that women everywhere are waiting to trap them with false accusations of rape, they know damn well they have to be bloody sure of consent.
If the media suddenly started reporting a small number of cases where teens were getting hauled in for sending/distributing pics, I think the perception would suddenly be that all and sundry were being targeted, fear of repercussions would spread and behaviour would change. Currently there are zero sanctions for what is not only criminal but very, very damaging to all concerned.
Have a massive campaign telling youngsters the law and leave them in no doubt that there is going to be a crackdown. If you break it, you pay.
I'm not sure you can effectively address the cause. Teenage boys are getting free nude pictures at the click of a button. But you can address the behaviour.
I don't think it would take long for pressuring girls to send naked pictures is seen as the unpleasant and sleazy issue it is.
Course, then there's the issue of porn.