It's done with slave labor.
It's called pig butchering. You kidnap people, hold them in Cambodia or whatever (lots of locations where local criminal gangs rule) so the locals don't bother checking for literally kidnapped slaves.
If police stop by, pay them off and make up a story about debts and punishment.
Then you use the slaves to scam others in pig butchering scams. If the slaves refuse, you beat them until they comply.
https://www.propublica.org/article/pig-butchering-scams-raid...
Btw this is also used as a sob-story tactic by the scammers if you eventually call them out after some time.
Thanks! That's a much better link and explanation than what I linked to.
So reply asking if they want you to notify authorities in their city. I doubt that the kidnappers are reading every message. And even if they are, better to let the kidnappers know that they are being encroached upon.
Just to clarify the terminology, pig butchering refers to the scam to steal money from fake romantic partners. The SE Asian kidnapping/slavery shops that run pig butchering scams are referred to as fraud factories.