Books! You can get paperbacks for under $10 apiece. Or, do they enjoy writing? You can get them each a journal. Do they have long hair? Perhaps barrettes or clips or headbands in their favorite colors?
Really cute colorful rainboots -you can maybe check a local department store and I see that there is a company called Sloggers here on Amazon that sells them for around $20 - -really cute and in all different colors!
They might enjoy the Love Comes Softly video series if they don't already have them. The first few are the best. I wasn't impressed with the last one. There's also a new Christmas one that I haven't seen yet. They are based on a book series, so if they prefer to read, you might choose the books instead. A pretty article of clothing (sweater, scarf, etc.) in their favorite color(s) might also be nice. Or if they like crafts, maybe some yarn in a favorite color with an instruction book and knitting or crochet needles.
Money or gift cards are allways a good fit. or a cupon book of I owe you. I owe you one ride to town I owe you one wash the dishes, pick the peas(or what ever chore she hates) I owe you 3 days of making your bed. I owe you one room cleaning These don't cost you anything but time either.
Knitting is making a big comeback and it is getting pretty popular with teenage girls. The "looms" are fun (I just tried one) and with one of these and a ball of pretty yarn you can make a scarf or a hat depending on which loom you use. The how-to videos are all over YouTube.
This link shows a set of different sized looms but all you need is one long loom for a scarf. I bought the Boye Large Long Loom and you can make a scarf or almost anything flat. I understand the round looms are easy for knit hats.
I have lots of teens on my list, including my own. Some of them I know well, and some not so well, but I've tried to know if they have a hobby or favorite activity. This year I'm giving earbuds with an iTunes card, a travel mug with a Starbucks card, or a water bottle stuffed with energy bars. Other ideas are gas cards for driving teens, fast food cards if they have a place they go during lunch... Just be sure to know what places are popular near them. These are all things that they'll use, use up or lose - not leave at home when they leave for college- I'm thinking of the parents too.