Agreed vole-woman, post watershed move may have been the wrong way to turn, but broadcasters will pretend to know the audience better than the audience know themselves.
As to what teenagers would watch, well that is a question!
I feel personally that there is often to much emphasis on the need for young peoples programmes to be "cool". Maybe thats part of it, but it also needs to be interesting, for example my friends who have no real interest in the natural world, will watch discovery channel, not because the programmes are supposedly cool but because they are interesting.
Get a fun presenter who appeals to the younger generations e.g. Chris Packham, Simon King or Nick Baker (some of my personal favs), some interesting critters, and have a good laugh. Autumnwatch Unsprung is a great example of the kind of larking about which might appeal to younger people
[please disagree other young people if you like
] Showing that wildlife is easily accessible might do the trick.
But alas channels aimed at teenagers are mainly about music, fashion and big brother, so broadcasters at some point would need to fit a new demographic into their busy schedludes (sorry im studying media production and media words keep popping up in my head
) so until the future these things will probably sit on the backburner...