We cannot blame teen girls for the ferociously sexist social environment they have no choice but to live in. Maybe what the girls in these YouTube videos are saying isn't: I don't feel pretty. Maybe it's actually: I feel completely powerless when it comes to my sexuality.
You're not ugly. Not in the least, so don't make those videos. Take them down if they are up. You don't need people to tell you how beautiful you are on there. You don't need to put yourself in the position to be judged that way.