If one's bike is stolen in the San Francisco Bay Area, there's a small but significant chance you can find it for sale at the Laney College Flea Market (e.g. [1]).
Bay Area here. Kid’s bike was stolen from driveway (lock clipped) and I found it online a few hours later. I called police non-emergency line and told them I had already set up a meeting to “buy it”; they offered to assist if an officer was available, and I brought a “tough” buddy in case not. Thief had a much bigger buddy hanging out ~50’ away (cop recognized them immediately). In the end: officer showed up, perp got arrested, and my kid got their bike back.
In LA county you aren't going to want your bike back. It's going to be spraypainted, missing components, thrown in the street, and perhaps made into a load bearing wall of someones ramshackle roadside home. Just insure your bike so you can write it off and get a new one without too much trouble or stress.
Yeah, Karim got raided a few years back but they couldn't make anything stick. Most people don't even record serial numbers on their bikes, much less register them with any type of organization that police can check for stolen bikes.
I pass by a very large cache of bikes every day on the way to work. The quantity ebbs and flows. Perhaps they're all procured legitimately, but somehow I doubt it. No one seems to be interested in investigating it because it's been going on for quite some time now.
[1] https://www.reddit.com/r/BAbike/comments/8mmrne/stolen_bike_...