Awww, I'm so sorry about your lost chickie! It must have seemed like a good idea to treat your new birds to some fresh air & outdoor fun. On the positive side, chicks can & do survive some extreme conditions, and there is a good chance that by daylight tomorrow you'll find it poking around the yard, looking for its buds. However... I'm afraid there's also a very good chance that this chick was nabbed by some predator right from the start. Did you watch it run off into the woods or is that just your theory? There is a whole long list of critters who consider young chicks a delicacy, they could have grabbed this chick from your yard or right after it ran into the woods. Usually chicks like to hang together, and will yeep & cheep if they're separated. But if these chicks were new to each other and to your yard, they may not have formed a good cohesive flock dynamic yet. I think you should keep the rest of them confined to some sort of pen until they get more used to each other and to your yard as home. Let us know what happens, I hope & pray for a positively miraculous outcome! Otherwise, don't blame yourself but file it under Lessons Learned The Hard Way, there will be many others on this forum who will benefit from what you've shared.