I visited a blog recently where they were discussing chastity for youth. As a Christian, I believe there is no absolutely no substitute for chastity. Youth need to understand that it's vital they do everything in their power to safeguard the sacred power of intimacy and procreation.
However, at the same time we are talking about the importance of chastity, we also must stress very strongly that no matter where a youth is in his or her life that through the Atonement they can be made pure again in our Heavenly Father's eyes if they go through a true repentance process, which is always painful but worth it. Some youth feel it's too late for them. Some believe they are beyond redemption and love. And that's simply not true, no matter the degree of their sin.
When I speak to young women, I always tell them about my teenage son, his friends, and the girls that interest them. These really wonderful, intelligent, spiritual young men don't run after the sexy-looking/immodest girls because they are uncomfortable around them. Or at least they NEVER brought them to my house. Interesting.
As a mother, I would always point out certain girls to my son and say, "Oh, I'd like you to bring her over sometime. Hmm, maybe not her. Her clothes are too tight." But is that fair, judging someone by what they wear? Well, it doesn't matter because regardless of fairness we are all judged by the way we dress and act. (And to oversimplify the point, I'd hate one of my daughters to miss out on a really great guy because she was wearing the wrong clothes that day.) Youth need to understand that at all times they are representatives of not only themselves, but of their family, their church, and their God.
Thankfully, modesty seems to be a maturity issue that most girls eventually understand and grow into.