I ended up calling our complex security company, and they sent out a security guy who I spoke to. He could hear the puppy from the hall, and to him he thought it was a woman screaming! He ended up calling our local Sheriff's dept to have them investigate. They said they were coming, but they never showed up.
I listened to the poor thing cry until after 1am. I then heard the neighbors finally come home at 2:30am. I couldn't believe they left a puppy - probably 12 or 13 wks max - home alone for 5+ hours. I felt sick all night. This morning I've emailed our Complex manager about the situation, and I'm waiting for local animal control to open so I can call and talk to them too. I don't ever want another night like that again. I felt so helpless.