I plotted an area for me to check starting tomorrow. (basically used google earth) The junk pile is a little over 200 ft away from the coop so it looks like just woods for my search and half of the radius is our house, driveway, and garden so it looks like it will be a quick search!! We have predators but we have been really lucky with them so far, the main rooster is missing a spur and a few claws from his run in with a possum a few months ago (my boyfriend finished the job the rooster started). After that run in he baited and killed any possum or coon that came close to the coop at night. I also found some tips for finding their nest...
http://www.muranochickenfarm.com/2013/05/12-tips-for-finding-guinea-nests.html
I quickly read through the article, I'd say it's very good advice. If you get close to the nest, they'll let you know with their body language. Don't rule out the junk pile, they love junk piles. Also, if something drug them off you might find remnants near places like that. Good luck, keep us posted on how the search ends up.