Yeah, big problem. Attention and identity are severely in demand right now. I have no idea what the answer is, but here's what I want to try: I think you start with corporate worship, because that's where God is God and we are His people. Then you build smallish, tight-knit communities around that; the trick then is to overcome geography.

$0.02.

It is a big problem, but it's not really one that we can address or that the kids can address. The issue at hand is that parents are failing to set boundaries for their kids. In the end, we have fried parents (running taxi service for however many kids) and kids that are constantly trying to keep up with expectations. Until the parents decide that this is not an acceptable lifestyle, that Christian fellowship is a real priority, and that what we're offering is worthwhile for their kids, the church will only be seen as one more competing time drain.

I have the same problem in one of my parishes. The strategy that I'm currently using is to focus on the few that are interested... Spend tons of time and effort providing quality interactions and community building with the kids that are invested. They go back and share with the others how incredible it is and then the next time around there are more kids involved. This past year, I was disgusted in the level of participation of the youth in community building and discipleship. After a year of throwing my energy at the few that are interested, I'm seeing others come around and an increase in participation. I agree with TaraJ, the issue is the parents and I haven't figured out how to address that issue, though I'm impressed with Rob Reinow and the Visionary Parenting series for parents.

Just a thought... I feel very strongly that I want my children to be involved in Christian fellowship/community because I know how important that was in my life when I was their age. I totally see the value there. Perhaps the parents aren't placing value on Christian fellowship because they themselves didn't experience that as a youth. It is perpetuating itself. So maybe a two pronged approach would work. Mrslouis's strategy of spending tons of time and effort on the kids that are there--plus try to identify some parents who had the Christian fellowship as youth and help them remember what an impact that had on their lives. Encourage them to be advocates with the other parents. People tend to listen to their peers, don't they? If one parent was talking up a great preschool there would be a clamour to get there. Maybe the same would be true for your youth programs. But they aren't going to come until there is a perceived value. We know it's there--we just have to convince them...

Unfortunately during this year it's probably too late to convince youth and/or parents to revisit their schedules; they already signed up for all those classes (and paying big bucks for them too). But I would try and talk about the importance of schedules and time management (time distribution ?) in a Christian home in the coming months. Parents are signing up their kids now for this summer, and depending on the activity, at the beginning of the summer for the fall.
I'm sure senior high students are trying to build a resume for college by having a lot of extra-curricular activities. There's no reason involvement in a church youth group couldn't be a great asset in a resume; it could have a catchy name, and some youths could even have titles (secretary or treasurer of the youth group, or music leader, or outreach researcher or something...), showing responsibilities instead of simple participation in sports or whatever.
For reaching the hearts of the parents I also highly recommend the Visionary Parenting series; the 3rd session specifically talks about how our schedule teaches our kids what is really important for us. Rob Reinow was just in Fort Worth last month to give a day seminar and absolutely blew my mind. An excerpt from his book God's Grand Vision for the Home:
"When your son or daughter leaves your home someday, which one of the following would you most want for them:
a) to be successful academically
b) to be successful athletically
c) to be successful socially
d) to be a person of faith and character.
Personally, I would like to have another option, "all of the above". But if you could only have one, which one would you choose ? You most likely said faith and character are most important. At least it seems like the "right" answer.
Let me change the question a bit. Which of the following parenting issues gets the best of your time, effort, money, anxiety and planning ?
Academics, Athletics, Social life or Faith and character development ? " end excerpt
You see where this is going, I'm sure.
I guess praying for God to open up the parents' hearts to this message beforehand would help too...