I think the hardest overall problem that American Christian teenagers face is navigating the mixed messages that get thrown at them on a daily basis. In my mid-20s and coming from a public school background, I personally witnessed a lot of teen violence, depression, anxiety disorders, anorexia, and other teen issues on such a scale that it was difficult for the school system to manage them. Those trends have sadly continued to increase.
This is why there's such a need for churches to reach out to teenagers and provide a welcoming environment and stability. In speaking with several teenagers at my church, here are some of the issues that church youth groups and churches in general may want to help teenagers address:
1) Self-Esteem/Role Model Issues-Finding Good Examples to Follow
Forming a sense of identity is one of the primary developments in the teenage years. There are problems in unrealistic ideals being portrayed in the media (models made to look skinnier using software, etc). Sexuality and alcohol abuse is being marketed toward younger and younger age groups, with many entertainers who should be role models for teens showing little to no responsibility for their position.
There's also this idea floating around out there that God only wants people who are "perfect" and have their lives together. This sometimes keeps teens from seeking God when they need Him most, not really knowing He does love them.
2) Evolution Being Taught as Truth, Not Theory, and How Alternative Viewpoints Are Treated
The promotion of evolution as doctrine instead of a theory, even though there are many scientists admit that it has holes in it, has had a major negative impact as well. In many public school settings, trying to offer your viewpoint as a Christian student is often suppressed. Obviously there's a major difference in attitude of someone who sees himself or herself as the creation of a loving God and someone who believes we're nothing more than a cosmic accident.
Watching Ben Stein's recent documentary "Expelled: No Intelligence Allowed" explains a lot as to why intelligent design is a legitimate and scientific objection to Darwin's theory and the reasons behind why scientists who research from an intelligent design angle are kicked out of academic circles for political reasons. In the meantime many students are having it drilled into them that they're descendants of single-celled organism that just spontaneously appeared from inanimate materials. It's interesting to watch how the evolutionary argument breaks down when Ben Stein starts asking hard questions as to how and why that "spontaneous" event occurred.
3) Lack of Knowledge of America's History
If you compare American history textbooks now to those from 20 years ago, there is a major difference. Very few teenagers realize today that our founding fathers asked for God's help with our nation and were very brilliant people. I think the watering down of our history for the sake of extreme political correctness has been a major disservice to our generations. A person can still find things on their own, but as adults only a small number of people are willing to make the effort. This lack of knowledge is providing some humor for the Tonight Show with Jay Leno (who is a good guy), but it's also very sad.
4) Morality Being Associated With Religion, So It's Not Commented On Anymore
It is scary to me that teachers today have to hesitate in making a comment on a moral issue because of the fear of getting fired for promoting a religious view. That's taken a lot of authority away from good people and has led to a lack of discipline in many cases.
As I move forward as an adult and begin to think about these issues as a future parent, this has become a very important issue to me. Our current teenagers need more adults to step up and start speaking up for them when they're in a hard position of speaking up for themselves. Financially supporting teen ministries (even if you don't have kids and/or are barely an adult yourself) can help a lot of with this.
It's also personally affected how I vote (both on a national and local level) and how much I make an effort to look into a potential leader's background before I vote for them. This isn't something that can be turned around overnight, but as Christians we do have the ability to change things for the better either from the national level down or the local level up. We can't forget that.