ST. PETERSBURG — Car thefts and burglaries have risen dramatically across the city in the last two years and for the most part, police say, kids are behind it.

In 2014, St. Petersburg police documented 1,418 auto thefts or burglaries, up from 876 in 2012. Officers made 600 arrests for the crimes last year, including 74 in December alone, said Maj. Paul McWade. Adults are usually the culprits in auto burglaries, he said, but when a car is stolen, 97 percent of the time a juvenile is behind it. In almost all cases, stolen or burglarized cars were left unlocked, police said.

"There are about 100 kids in our city that are doing all of these crimes," McWade said.

One 17-year-old spent nine months in jail last year, but used the three months he was free to steal nine cars and car-jack another, according to police. Usually, the thieves are between 13 and 19 years old, but McWade said police have found some as young as 8 or 9 involved.

It is not a chop shop scheme, and in most cases, McWade said, the teens are not stealing cars for profit. They take them for joy rides, sometimes flying 80 mph through residential neighborhoods.

"These 14- or 15-year-olds are driving recklessly through our city," McWade said, warning that eventually they are "going to hurt or kill somebody."

They leave vehicles in parking lots and return to drive them the next day. A number of cars have been used in other crimes around Tampa Bay, such as home burglaries or shootings among teens in feuding neighborhood groups.

"They've been beefing lately, and they've been shooting at each other," McWade said.

The best thing car owners can do to avoid being a victim of theft is lock their vehicles, police said. People should also remove extra keys or fobs from inside their cars. McWade said some owner's manuals have valet keys, which teens will find and use to start vehicles.

A group of teens might drive to a neighborhood in one van, then dash along the street, tugging at door handles to find which cars are unlocked, according to McWade. The second way they steal cars is called "flagging." A thief will stand outside of a store at night, look for people to pull up and leave their headlights on or their car running, so the keys are inside. Then they hop in and drive off.

Since police see the same suspects over and over, teens have started quickly sticking tint film onto the windows of the cars they steal, making them harder to spot. They also take license plates, so McWade advised drivers to frequently check their tags. Car thieves find a vehicle of the same make and model as the one they stole, and switch the license plates between the legal car and the stolen vehicle.

McWade said cars are stolen from all around the city. Often, he said, "kids from our city go into other cities taking their cars and bringing them back to us or vice versa."

St. Petersburg police conduct covert stings and track the thieves in an attempt to get the cars back. They have hung tags on doors, warning drivers of crime and offering tips on how to keep their vehicles safe, and they've asked car dealerships to advise new buyers of best practices.

Car theft is a crime of opportunity, McWade added. He thinks believes the recent surge is likely the result of word spreading about how easy it is to steal a car. Because the alleged perpetrators are so young, he said, they are sometimes released the same night or the day after their arrest.

"They keep getting out and doing the same crime," McWade said.

Contact Zachary T. Sampson at zsampson@tampabay.com or (727) 893-8804. Follow @ZackSampson on Twitter.