Posing teenagers is a little trickier as they tend to be more self-conscious. Trickier but not impossible. What you need to do is to pull off a good photo early in the session to build trust. If they aren’t in for a smile, and most teenagers aren’t, skip right over it and go with a serious look. You can go back for smiles after you build that trust, but your first goal is cranking out a photo that makes them look cool.
To do this, go with the basic rule first: “Neck like a giraffe and chin down a hair.” After that have them fold their arms. Alternatively, you can have them swing their arms side to side very slowly. Either of these give the arms something to do and makes the body look more fluid and less stiff. Stiff limbs look awkward, loose limbs looks relax and improves your odds of some solid shots.
Finally, notice again the clothing. Simple designs. Sure, you can mix them together into something more complicated but so long as it is a mix of solid colors or simple patterns. Anything else and you risk losing your composed image to the complex and distracting clothing.