I searched the house once again before leaving for work, again nothing. Left food out in the standard place. Just as my son came out with his school bag, he yelled, "PAPA!!! CHICKENS!!"
They came running across the lawn from the neighbor's yard as fast as they could and made a bee line for the food. The best theory I could come up with is that my neighbor (the one who gave me the chicks in the first place) has a six foot chain link fence around his yard that he never closes the gate to. They must have been over there when it got dark and couldn't find the way out.
They were too hungry to let me catch them (they know that means going inside) so I had to leave them out again for the day. Tonight I will finish the run. Leaving them to their own devices is just too stressful.
Godzilla and Mothra are home safe and sound. THANKS TO EVERYONE FOR THE ADVICE/FEEDBACK/SUPPORT!!!!