We dont know the size of the trap or whats trying to get in. First its probably a rat, possum, skunk. If it was a racoon it would probably already gotten in.
So lets try a rat first. i have a feeder on the floor for some old hens that are free ranging. Whatever pellets they leave behind by the end of the day, I sweep them in a little pile and put the live frap over the pile, behind the trip peddle.
i usually catch the rat if there is one around. If they are trying to get in the coop via tunnel, let them get in then use a spring type trap that is baited with good stuff. The best rat bait that really draws them in is very crispy bacon tidbits mixed with peanut butter.
Once you have the trap baited and in the path (feel free to modify to set the trap solid), then cover with a bucket so a chicken doesnt get snapped.
Another way that is proven killer is an old 1 1/2 size leghold jump trap. This works in the feed storage area where no critters are supposed to be. Use an old sauce pan and fill it with an inch of feed and set the trap right on top. the rat will hop right over and land square on the pedal which will grip it midsection.
If its a skunk, dont try the last method!!!!!