Yeah, that sucks. I had the same thing happened except the chicken vanished without a trace. Ended up finding some feathers in a nearby tree. I spent the next two nights going out every now and then to see what it was. The third night was successful. I found a raccoon in the pen poking around.
A spotlight and .22LR round to the vitals fixed the problem right up. I repaired the damage to my netting and havent had a problem since. I have loads of these buggers, but this is the only one I have 'dealt' with. The rest are good to go as long as they dont get into the run. If I catch them there, there is no mercy. Im a regular hunter and conservationist and don't like killing something just to kill it, but sooner or later you have to draw the line. Its just part of the game of chicken owning.
Rest assured, the coon WILL come back. Maybe not tonight, but soon.