"It's just an extension of what happens in Mexico," said Armando Garcia, assistant special agent in charge of U.S. Immigration and Customs Enforcement in Arizona, where the trend first appeared five years ago and has escalated to an average of one case being reported each week.
Investigators believe virtual kidnappers get the names and phone numbers of immigrants' families either by buying them from smugglers or by posing as helpers who can connect illegal immigrants with smugglers in Mexican border towns.
One family paid $7,000 before calling authorities about the scam. Once a ransom is paid, the criminals will often ask for more money and sometimes even demand that families cover the cost of the kidnapper's cell phone.
The kidnappers are convincing. They speak good English and use cell phones with a Phoenix area code so it looks like they are in the Arizona capital, even though they are probably making the calls from Mexico, where the extortion money is often sent.
Virtual abductions have also been reported in San Diego, where immigration agents investigate two to three each year, said Lauren Mack, a spokeswoman for that city's office of U.S. Immigration and Customs Enforcement.
It's not hard to trick families into believing an actual kidnapping has happened.
Relatives of illegal immigrants know that human trafficking is a violent business in which customers who have already paid their smuggling fees are sometimes held captive while smugglers try to squeeze more money out of friends and family.
Immigrants aren't the only ones risking abduction. Since the beginning of 2007, Phoenix has had more than 560 kidnappings in which drug and immigrant traffickers, and their families, have been abducted by fellow criminals and held for ransom.
Immigration agents are stumped about why Arizona is seeing an increase in virtual kidnappings, and they believe the number of cases is probably higher because some cases go unreported. Immigrants and their families don't want to risk being deported, or they are embarrassed about getting ripped off.
Virtual kidnappings also drain law enforcement resources because investigators have to assume that the ransom calls are valid.
A telltale sign of virtual kidnappings is an unwillingness of the scammers to put the supposed abduction victim on the phone. Smugglers who are really holding someone hostage will often let family members speak to the relative.
Immigration agents recommend being skeptical of ransom demands if the caller does not allow relatives to speak with family members who are supposedly being held captive.
In one case, a woman who got a call that her ex-husband was kidnapped called the scammers' bluff, saying she didn't want to speak with them if she couldn't speak with him. The criminals started calling the man's girlfriend.
Virtual kidnappers will eventually change phones and move on to the next victim if they can't extort money from a family.
"Maybe it's working with 10 out of 100 people that they call," said Garcia, the Arizona immigration agent.