At one time it would be contacting the City Council. These days there is such a backlog, I don't know what would be best.

I would not suggest tearing it down yourself, there could still be an owner and you could get sued. As hard as it can be to imagine, it could happen. There would also be potential hazardous materials to get rid of, and a basement to tear out and fill back in.

Its not as easy as taking a sledgehammer to it. I've been tempted to do that to a few buildings myself.