Spreading general awareness could be the most important thing to do. All these places, these "underground slave houses," operate right under our noses apparently -- smack dab in middle class neighborhoods, in "massage parlors," etc. Since I've learned more about this I've been keeping a close eye on places I've always sensed were a bit off kilter, looking for potential warning signs (according to my understanding of what the warning signs even are -- maybe we should discuss those here).
I would normally suggest that people involved in local mafias or drug-dealing gangs should be most educated on this issue since they would be "more likely" to encounter the people in charge of these operations, but that would very likely be a misconception on my part; this phenomenon could be hiding in plain sight, and everyone has a duty to take an interest in their own environment and check for whatever warning signs there might be.