No pressure to be "super tech-y," teens just like hanging out and trying new things. Just put out a bunch of stuff, make some fun signs, and they'll like it! I replied to the HS thread and there are some ideas on that thread. We're a tech HS so our kids are using tech, all day - that's why we do a low-tech or no-tech TTw. Anything to get them into the Media Center! Legos, adult coloring, mazes, origami, sudoku, zentangle, giant cardboard Jenga (2 sets @ $20 each, Amazon). Old board games, upcycling old computer "stuff," black-out poetry from old encyclopedias, taking apart an old computer CPU (tower - they love this!),selfies with pipe cleaner mustaches or crazy glasses (Yes, even HS students like these "old school" play things). If your teens start posting pix on their social media, it will bring others in. We also have giant checkers set with prizes (snack bags) and 3 wooden Jenga sets that they put together and build really tall towers. Badge and button making also good - we use old comic books and they make small buttons for their backpacks. Hope this helps. Just jump in and they will come!
Last year we put out materials to make a pocket green screen (http://www.instructables.com/id/Pocket-Green-Screen/) and they turned out really cool! I'm also a big fan of paper circuits. All you need is tape, scissors, coin cell batteries, LEDs, and inexpensive copper tape. http://highlowtech.org/?p=2505
The nice thing about these is that you can put out a little at a time and they don't require anything expensive, so you don't have to worry about them walking off.