I mostly stumble upon them by accident while on my way to do something else. I’ve also done a lot of traveling on account of only dating people over long distance, so I’ve been to a lot of different cities in the eastern half of the United States.
There are however a few tricks I’ve discovered for locating spots on demand. Try scrolling around Google Maps’ satellite images of your area
and looking for rooftops that are rusty, overgrown, or partially caved in. Also, it’s good to just wander about in general. Walk or drive down a road you’ve never been on, the more decrepit-looking the better. Go to places where real estate is cheap, where abandoned buildings are unlikely to get demolished. Keep your eyes peeled for graffiti, as it’s often a good sign of areas without much nearby traffic or human activity. And any time you go somewhere new, take the opportunity to explore your surroundings.
The bottom line is just to always keep your eyes peeled; you never know when you’re going to come across a great find.