• Thieves are targeting certain makes and models of 2010-2021 Kia and Hyundai vehicles that use a mechanical key, not a key fob and push-button to start the car.
• The thieves are mainly young teens who use a USB cord to hot wire the car.
• They post videos stealing and driving the cars on social media using the hashtag "Kia Boys" — which has more than 33 million views on TikTok.

A dangerous challenge spreading on TikTok and other social media platforms has car owners and police departments on alert across the country — challenging young teens to steal certain cars off the street using a USB cord.

The target? Certain makes and models of 2010-2021 Kia and Hyundai vehicles that use a mechanical key, not a key fob and push-button to start the car. Investigators tell CNBC the trend started last year and the number of cars being stolen is continuing to surge across the country. 

In St. Petersburg, Florida, police reported more than a third of all car thefts there since mid-July are linked to the TikTok challenge. Los Angeles officials say the viral trend has led to an 85% increase in car theft of Hyundais and Kias compared with last year.

The story is the same in Chicago, according to Cook County Sheriff Tom Dart.

"In our jurisdiction alone, [thefts of certain models are] up over 800% in the last month," he said. "We see no end in sight."

The trend challenges teens to steal a car off the street by breaking into the car, popping off the steering wheel column and hot wiring the vehicle using a USB cable, similar to the wire used to charge a phone. 

"The viral nature of how this has taken off on social media — it's accelerated this like we've never seen," Dart said. "[The perpetrators are] doing it in 20 to 30 seconds. It literally is as old-fashioned as you can imagine."

Dart told CNBC the thieves are mainly young teens — some, not even old enough to legally drive. The stolen cars are often used for joyrides, or used to commit other crimes and then abandoned on the side of the road, he said.

"We had an 11-year-old who was one of our most prolific stealers … the notion that they can drive is a fantasy," Dart said. 

The thieves post videos online of stealing and driving the cars, using the hashtag "Kia Boys" — which has more than 33 million views on TikTok. The social media company said in a statement it "does not condone this behavior which violates our policies and will be removed if found on our platform."

Illinois resident Karen Perkins said her 2019 Kia Sorrento was stolen from in front of her apartment on Aug. 6.

"I looked out the window and realized my car was gone," Perkins said.

Days later, she was in a rental car at a red light when she said her missing Kia drove right past her.

"I saw a teenage boy sitting in the front," Perkins said. "I drove around the block … five kids actually jumped into my car — that's when I started to panic — like I'm going to lose my car forever."

Perkins tells CNBC she went on a hunt to track down her Kia. Hours later, she found it deserted on the side of the road and called police. She said the abandoned Kia was left heavily damaged. 

"They crashed the front of my car … they damaged the bumper," Perkins said. "They even wrote on the top of my ceiling … it says 'hot car.'"

Tom Gerszewski, a Milwaukee, Wisconsin-based filmmaker, tracks the viral crime spree on his YouTube channel in "Kia Boys Documentary," which has already topped 3.7 million views.

"This is what they do for after-school entertainment," Gerszewski told CNBC. "They don't really have much of a sympathy for the people that they're doing this to."

Ken McClain, an attorney in Missouri, says some of the blame for the stealing spree falls on the automakers — Kia and Hyundai — claiming the companies built cars that are too easy to steal.

McClain calls the issue a "defect." His firm has filed class action lawsuits in 12 states so far: California, Colorado, Florida, Kansas, Illinois, Kentucky, Iowa, Minnesota, Missouri, New York, Ohio and Texas. He's also preparing to file in as many as seven other states.

"We're receiving dozens of calls a day," McClain said. "The manufacturer[s] ought to be paying for this."

Kia and Hyundai weren't able to comment on how many vehicles are included in the make and model years and would potentially be at risk.

A Kia spokesperson said the company is concerned about the increase in thefts and has provided steering free wheel lock devices to law enforcement officials in affected areas.

"It is unfortunate that criminals are using social media to target vehicles without engine immobilizers in a coordinated effort," the spokesperson said.

"While no car can be made theft-proof, criminals are seeking vehicles solely equipped with a steel key and 'turn-to-start' ignition system. The majority of Kia vehicles in the United States are equipped with a key fob and "push-button-to-start" system, making them more difficult to steal. All 2022 Kia models and trims have an immobilizer applied either at the beginning of the model year or as a running change."

A Hyundai spokesperson said the company is pursuing a similar effort to distribute steering wheel locks and that the company will begin selling a security kit next month.

According to Dart of the Cook County Sherriff's Office, the old-school wheel lock anti-theft devices could go a long way to thwarting the thefts.

"It makes it nearly impossible to maneuver the car," he said.

— CNBC Specials Page Peter Ferrarse contributed to this report.