They were trespassing at 1 in the morning, and given the time of night could have been drinking a bit as well. So it's really no surprise that no one would call the police when one person could not be located. The idea that he had been seriously injured probably wasn't even a consideration at that point. They probably just assumed he had left, or was still hiding.

Even if they had called the police, I can imagine how that call might go. "We're in our early 20's and playing hide and seek in an old warehouse, but can't find "Joe". The likelihood of an officer ever showing for a call like that on a Friday night in Detroit is near zero.