You should inform a trusted adult - if you manage to get away from the person pressuring you.
If you find that it's hard to move away from them, then you should make excuses that allow you out of the situation (like saying that you need to go to the bathroom or you left something somewhere or something reasonable that convinces them that you're not trying to leave them)
If the situation is violent, learning how to defend yourself - or where to attack the person (like their eyes or nose) can help you out of the situation. If you think it's serious enough, contact police.
Hope this helps you a little it.
