First of all, let me say that my experience is with teen boys, though girls have come to the parties we've given. The party took place from 6 p.m. until Midnight. Surprises are great, but I've found that asking what kind of theme a teen wants avoids a lot of misunderstandings. This year I thought my son would love everything in his school colors, but come to find out he wanted University of Michigan colors. He also requested a big cake and balloons. Those were things I could work with! Our decorations consisted of:
-A balloon bouquet plus 2 extra for the sign at the end of the driveway.
-Blue and Yellow plates, napkins, and plastic forks and spoons.
-Blue and Gold beads on the table for the kids to take and wear.
-Gold confetti sprinkled on the table.
-Blue table cloth with a yellow table skirt.
-Blue and gold hat for the birthday teen.
Don't underestimate how silly teens can be, even if you think of them as moody at times. We gave my son the hat, googly eye glasses and the beads, which he wore during the party. The other kids wanted a turn with the glasses and they ended up being a dollar well spent for entertainment. I bought a bunch of the beads at the dollar store in our town, and every teen had them on by the end of the night.
We turned the garage into an area for Guitar Hero and Rock Band. It wasn't anything fancy, and my two sons and a few of their friends set it up before the party. Our camping sun canopy served as the "music station" with a stereo and speakers. A couple of the boys took turns changing the music. As a group they played a soccer game early on, but later mostly talked or played Guitar Hero. Teens usually have enough energy to entertain themselves if you provide music and a few games.
Once it started cooling off and the sun was going down we let them have a bonfire. I had marshmallows and hot dog forks to roast them over the fire. We asked the kids to bring lawn chairs, but I also had old blankets on hand. We left them alone for the most part, but we could see the fire pit from the house, so it was easy to keep an eye on everything. We didn't have one problem the entire night, and everyone was well behaved. When midnight got closer everyone started going home on their own, but we did make make the rounds finding out which boys were spending the night, and who needed a ride home.
I know many parents struggle with birthday parties as the kids get older, but I think we put pressure on ourselves to make it a bigger deal then it needs to be. Kids generally just want to be the focus of the special day, and have fun with their friends.