For a teen boy, you may just stick with decorating in his favorite colors. You may want to stay away from a theme. Put up some balloons in his favorite colors, have some pizza and drinks, and some music.
Most of the time teens are not into theme parties. Give them pizzas, movies and video games and they are good to go. If you insist on a theme choose a popular teen movie or video game. Play the movie and have food that is in the movie or goes along with it.