It's not people who were directly found using them, but how many cases the law enforcement actually searched flock data. Whether or not that data actually caused the law enforcement to find anyone is going to be hard to actually track.

https://www.khou.com/article/news/local/dps-license-plate-readers-find-abducted-children-houston-flock/285-69e26c5f-68c0-45a5-8c32-e4052760aa1b

You have to look at individual cases to see if the cameras made a big impact on the case