This is an excellent resource for youth who feel as if they are out of alternatives.
Ellen DeGeneres' has answered the question, "What can we do to be supportive?" by directing people to this website. It is positive, helpful, informative. And, if you know a young person who feels conflicted or confused about their personhood/sexuality...this is a confidential resource to help.
TheTrevorProject.Org and resources that I am recommending are great recommendations to make in the event that you, on your own, "don't know what to say."
On that note, I have a suggestion for a sentence that works exceptionally well, particularly when you mean it from your heart,
"I love and accept you just as you are."