Don't panic. A nuclear device was in fact lost, but that device is used to determine the density of the ground, and not hold the world at bay while you laugh on the Big Screen at the UN. Still, it's potentially dangerous and the people who lost it would very much like it back.
What seems to have happened was a Troxler 3440 Nuclear Density Gauge fell off the back of a truck travelling on I-81 somewhere between mile markers 17 and 24. That means it could be in West Virginia... or maybe Pennsylvania. The people who lost it aren't entirely sure.
That Troxler 3440 seems like a pretty amazing device. From what I can gather, the nuclear materials send out Gamma rays which are sent into the soil, and then the the bounce back is sensed. I think. It sounds sort of like a Gamma-ray based radar or sonar system. These things are commonly used by construction crews and surveyors, and I'm pretty sure that if you hold it up to your genitals for long enough, it'll turn you into the Hulk.
So, if anyone sees a yellow box with buttons on it and a tall, protruding handle assembly, see if it smells like Gamma rays and then follow these instructions:
Anyone who finds the gauge should leave it alone and report the location to DEP during normal working hours at 717-787-2480 or 412-442-4227. After normal working hours and on weekends, call 1-800-541-2050 or 412-442-4000. In the event of an emergency, dial 911. A trained individual will be dispatched immediately to recover the gauge.
There's even a reward! Maybe it's big enough to afford a Troxler Nuclear Density Gauge of your very own!
(Hat tip to @ellengilmer!)