Thru-hikers make up a very tiny fraction of backpackers. You will have much more luck locating them at a site that is designed to meet their very specific needs, such as whiteblaze.com or through the mailing list run by pcta.org.

If you really would like to persuade some thru-hikers to assist you, I would also suggest offering them some sort of monetary support or direct physical assistance, such as helping them to resupply more easily on the trail. Personally, if I were thru-hiking this year and all you had to offer me were further complications for what is already a very demanding activity, I think I'd go out of my way to avoid you as a waste of valuable time and energy.