E-cigarette maker Juul Labs Inc. is under criminal investigation by federal prosecutors from the US attorney's office in the Northern District of California, according to the Wall Street Journal, citing people familiar with the matter.

While the focus of the probe is unknown, the fast-growing company has come under heavy scrutiny by state and federal officials over a rapid rise in vaping among teenagers - with the Federal Trade Commission (FTC), the Food and Drug Administration (FDA) and several state attorneys investigating the company's marketing practices. To top it off, the Trump administration announced earlier this month that it was planning to ban most flavored e-cigarettes.

The FTC’s probe is focused on whether Juul used social-media influencers and other marketing to appeal to minors, while the FDA is conducting a more wide-ranging investigation, covering marketing and outreach as well as the high nicotine content of Juul’s refill pods. -Wall Street Journal

The San Francisco-based Juul claims that it has never marketed to teens - despite a Stanford Research white paper which concluded that the company's marketing "was patently youth-oriented."

In the summer of 2015, Juul’s product launch coincided with sampling events in major US cities. Good-looking young people distributed free Juuls at movie and music events. “The principal focus of these activities was to get a group of youthful influencers to accept gifts of Juul products,” the report states, “to try out their various flavors, and then to popularize their products among their peers.” The same year, Juul launched a “Vaporized” campaign. Again, its colorful ads — blasted out on billboards, in magazines, and on social media — featured happy, playful 20-something models. -Vox

According to the Journal, "While cigarette smoking has dropped among teens, nearly 28% of high school students this year said they had used an e-cigarette at least once in the past 30 days, up from 21% a year earlier, according to a recent federal survey."