Yeah, I'd advise you to just avoid this whole place entirely.
I've seen your sister around, but I've never properly met her - still, it's nice to meet you. I'm Cole, and I live on the eighth floor which is currently haunted by the ghost of your sister's dead boyfriend.
New York is a great city, but it can get pretty crazy. I still haven't gotten all my sight-seeing out of the way.
Concerning the building... I'll echo everyone else's feelings and say avoid the elevator. Weird things tend to happen, especially around the anonymous posts. Just... be prepared, I guess.