I think this is great! I grew up in Southern NJ, very close to Philly. I used to find hundreds of wild box turtles every year both in the field and on roadways in NJ. My grandfather had a trailer in the Poconos, and we would travel throughout the beautiful state of Pennsylvania throughout the year. I'd find Bog, Spotted, and Wood turtles while sharing my time trout fishing in your clean, clear streams. Now that you mention it, I don't think I ever found a box turtle in PA!! I certainly should have, with all of the traveling about.
I think you have a tough task ahead of you, with their apparent scarcity. I'll give you a few of my box turtling tips. Box turtles always seem to show up when you least expect them. About the time you give up...boom, there one is. I've spent hours searching damp woodlands only to save a box turtle from certain smashing on the drive home.
Rain, rain, rain...eastern box turtles love rain! Your hot times are going to be during periods of rain, as well as the hours following a shower. The temperature that they seem to thrive in is about 73F to 83F. If it's much cooler or warmer than that, they won't move a whole lot. I know it doesn't get scorching in PA, but if you have a few days of very hot temperatures...like approaching 90, and then you have an afternoon thunderstorm, they should start moving en masse. Also, mornings when it has rained all night or all the day before and then the sun comes out and the temperature begins to rise, they should come up to forage when the temperature is right. I really think that this is when they'll be active for the longest period. The ground is soaked well, the slugs and worms are moving about, and they often seem to stay active for the greater part of the day following the rain.
Another thing you want to look for is food sources. Obviously, bugs are everywhere. Box turtles consume vast quantities of bugs. But, they also love berries. Look for wild blueberry bushes and stands of wild raspberry. A box turtle will often camp out nearby.
People are going to think that I'm crazy, but I can sometimes track a box turtle. Place one on the ground, sandy soil works the best. I know you don't have a whole lot of sandy soil where you are. Anyway, the box turtle will make tracks. They are very distinct. Rains will smooth out the ground. Open ground is usually found on walking and biking trails. After the rain, the turtles will come out and make tracks along the paths. When you get good, you can even tell which direction the turtle is traveling. For now, just search both sides of the path. Turtles usually don't move too far. Also, I've found that turtles make little tunnels...I think the technical name is "form". They are shallow grooves in the leaf litter usually 4 to 5 inches wide. The turtles will dig through looking for worms and other forage. I've found these literally 10 feet in length, meandering about, with a turtle dug in at one end. When a box turtle is buried in leaf litter, it is virtually invisible. This is how they remain for the majority of their lives. Looking for these forms could help point them out.
One more thing. I know this is terribly long, but you seemed desperate and I'm hopped up on coffee
If this area you are searching has roadways...do something called road cruising. Before and again after you search, drive all of the roads that you reasonably can within your target area. If you're doing it at the correct times, I can promise you that you'll find more on the roads than in the woods. You can literally walk by a box turtle sitting at your feet in the forest, they blend in amazingly well. But, they stick out like a sore thumb on the roadway. Good luck, and please...bring a digital camera, take some photos for us, and post them on this site. I'd love to see a wild PA box turtle! Also, you'll most likely stumble across one of my favorite animals...the Wood turtle. I'd love to see photos of them also. We can walk you through the process of loading a pic on this site when the time comes. Keep us updated on your progress. I travel to the Poconos once yearly, and my wife and I would love to stop and help you with your search if it's not too terribly far from us. My newborn also loves the woods! Daddy's girl 