LOS ANGELES -- The caller who rang Valerie Sobel's cellphone had a horrifying message: "We have Simone's finger. Do you want to see the rest of her in a body bag?"
Then came the sound of her daughter, screaming in terror.
"She called me Mom (and said) 'I'm terrified, please help,' " Sobel recalled.
In the hours that followed, the kidnappers talked her into wiring $4,000 for ransom. Only later did she find out there had been no kidnapping. It was a scam.
"I was in bad shape for days," she said.
On Tuesday, police and federal agents warned that so-called virtual kidnappings are on the rise, and dozens of people already have found themselves terrorized into giving money to con artists.
Los Angeles police alone have received more than 250 reports of such crimes in the past two years, and people have wired more than $100,000, said Capt. William Hayes, who commands the Robbery Homicide Division.
By comparison, actual kidnappings for ransom are rare. Los Angeles police typically receive 10 to 15 cases a year, including kidnappings performed by other family members and acquaintances, Hayes said.
In the fake kidnappings, the callers demand that the victims remain on the phone so they don't have a chance to call their loved ones, officials said.
"If you get a phone call like this, immediately hang up," Hayes said. "Contact that loved one."
The FBI began investigating a spurt of cases in 2013. A multiagency probe dubbed Operation Hotel Tango identified at least 80 people in several states who had received such calls, although not all sent money, said Gene Kowel, acting special agent in charge of the FBI's criminal division in Los Angeles.
However, many of the crimes go unreported, he said.
"It's fair to say there have been thousands of calls made to U.S. victims, primarily from Mexico," he said.
Last week, a Texas woman became the first person in the nation to be indicted in connection with a virtual kidnapping scheme. Yanette Rodriguez Acosta, 34, of Houston is charged with wire fraud, conspiracy to commit wire fraud and conspiracy to launder money. She is facing up to 20 years in prison for each of 10 counts if convicted.
The indictment alleges that Acosta and her partners used Mexican telephone numbers to call people in Texas, California and Idaho. They allegedly fooled people into giving them tens of thousands of dollars either through money drops or wire transfers.
In some cases, the scammers choose area codes and make cold calls, hoping to catch an unsuspecting victim, officials said. In others, the crooks may use social media to obtain names of children and other facts that can be used to frighten specific victims.
In Sobel's case, she believes the phoney kidnappers obtained her daughter's voice, perhaps from her voicemail, and then altered it."I was convinced that this was real," she said.
Fear for a child's safety can override skepticism, authorities said.
Even Los Angeles Police Department Sgt. O.C. Smith was victimized. Smith said he received a cellphone call about two years ago while driving on a freeway.
"There was a woman ... screaming 'Daddy, Daddy help me. I'm in a van being taken somewhere,' " Smith said.
Although he didn't recognize the voice, Smith said he couldn't take the risk that it was his daughter. The callers threatened to "put a bullet in the back of her head" if he didn't pay a ransom, Smith said.
He talked the phoney kidnappers' ransom demands down from $1 million to a mere $350, although in the end he never paid. While on the phone with them, he managed to flag down Torrance, California, police officers who were able to call and verify that his children were safe at school.
