Likely sex workers, they are common in third world countries, often smuggled into america with a price, usually to sell themselves sexually to pay their debt to their smugglers. When they fail to deliver on their promise they dissapear.
Others may be illegal families, people not on the census records, people who no one in the govt would notice dissapearing. If an entire family was kidnapped, they could sell the males as either laborors or sex slaves depending on the buyer, and the women as sex slaves, the children especially females could sell for tens of thousands a pop to wealthy pedophiles. It is a business that generates alot of wealth.
I had to go through numerous briefings on human trafficing in the army, most originate from poor countries but some in the us, they usually either trick them by granting passage into the us for exchange in their services, to flat out kidnapping aiming for those in countries with poor census records or in the us aiming for those who have no census records in the country.
