I am a 16 year old. To be honest, most teens wouldn't handle the site. The requirement for an understanding of mathematics, logic, and science are beyond the reach of most, and the desire of most of the rest. That said, I have introduced two friends of mine to HPMOR and they have taken to it, and I am leading them towards Less Wrong. On the other hand? I don't know how many adults would handle less wrong either. If you want my advice on how to be more appealing to teenagers, it is relatively simple.

Link everything, so that someone who doesn't understand can follow your links and find out. Useful more for teens than for adults, it is still good practice. Few intelligent teens will tolerate a teens area for long.