North Carolina’s attorney general is launching an investigation into Puff Bar, placing new scrutiny on the e-cigarette that has unseated Juul as the most popular vaping brand among children and teens.

The probe is part of the state’s broader inquiry into the e-cigarette industry, including manufacturers, distributors and retailers who sell near North Carolina schools, said North Carolina Attorney General Josh Stein.

“We’re...

North Carolina’s attorney general is launching an investigation into Puff Bar, placing new scrutiny on the e-cigarette that has unseated Juul as the most popular vaping brand among children and teens.

The probe is part of the state’s broader inquiry into the e-cigarette industry, including manufacturers, distributors and retailers who sell near North Carolina schools, said North Carolina Attorney General Josh Stein.

“We’re concerned that the vacuum that has been created by Juul now following the rules of the road is being filled by other companies, and Puff Bar being one of the most significant,” Mr. Stein said in an interview Tuesday. He said his investigation would examine Puff Bar’s business model and business practices “to ensure that they are in compliance with the law and not contributing to widespread teen vaping.”

Lawmakers, regulators and public-health groups began raising concerns about Puff Bar last year when the use of its fruity, disposable vaporizers soared among young people. Federal regulators tried to force Puff Bar’s products off the U.S. market. But the brand earlier this year reformulated its e-cigarettes, replacing tobacco-derived nicotine with synthetic nicotine in a move that company executives said was intended to place the vaporizers outside the Food and Drug Administration’s jurisdiction.

Puff Bar didn’t immediately respond to requests for comment Tuesday.

The company’s co-CEOs, Patrick Beltran and Nick Minas, told The Wall Street Journal last month that they were doing everything they could to prevent underage use of their products. They said the rise of youth vaping was the result of lax enforcement of smoke shops that they said are selling e-cigarettes to minors. They added that counterfeiters have contributed to the problem by flooding the market with Puff Bar fakes.

North Carolina Attorney General Josh Stein said the investigation into Puff Bar is part of a broader inquiry into the e-cigarette industry.

Photo: Julia Wall/The News & Observer/Associated Press

Puff Bar’s vaporizers are similar in shape to the market-leading e-cigarettes sold by Juul Labs Inc., but Puff Bars are disposable and come in a wider array of flavors, including watermelon, lemon ice and blue razz. They are sold online and in stores for as little as $9 apiece.

Some 26% of high-school e-cigarette users said they used Puff Bar, according to a federal survey conducted earlier this year. Among middle-school vapers, 30% reported that their usual brand was Puff Bar.

In addition to Mr. Stein’s investigation, Puff Bar faces a probe announced last week by the U.S. House Oversight Committee’s Subcommittee on Economic and Consumer Policy. And the FDA has said it is looking into whether it can assert jurisdiction over Puff Bar and other e-cigarette makers that are now saying they use synthetic nicotine.

Juul was the most-used brand among children and teens for several years. Its popularity among young people dropped after it halted sales of its sweet and fruity flavors and took other steps to prevent use of its products among youths. Juul Labs in June agreed to pay North Carolina $40 million to settle a lawsuit brought by Mr. Stein, alleging that the e-cigarette maker had targeted underage users. Juul didn’t admit wrongdoing as part of the settlement.

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Mr. Stein said Tuesday that he was filing a new, separate lawsuit against Juul’s co-founders, James Monsees and Adam Bowen, who weren’t covered in the settlement. They didn’t immediately respond to requests for comment.

In February 2020, the FDA implemented new restrictions to curb youth vaping, barring sweet and fruity flavors in reusable e-cigarettes such as Juul. Those restrictions didn’t apply to disposable devices like Puff Bar.

In July of last year, Puff Bar halted its sales shortly before the FDA ordered the brand’s products off the market, saying they hadn’t been authorized by the agency.

Puff Bar resumed sales on its website in February, saying it had changed its e-cigarettes’ ingredients. The FDA regulates tobacco products and smoking-cessation devices such as nicotine gum; synthetic-nicotine vaporizers don’t fall under its purview.

Mitch Zeller, director of the FDA’s Center for Tobacco Products, speaking at a tobacco industry conference Tuesday, said that he was concerned about e-cigarette makers that had switched to synthetic nicotine to avoid the agency’s oversight.

“We are concerned about what this means for product regulation, for the public health, and with a product like Puff Bar proudly proclaiming its use of synthetic nicotine, being the No. 1 brand for kids,” he said.

Write to Jennifer Maloney at jennifer.maloney@wsj.com