SAN FRANCISCO -- The Food and Drug Administration is now reviewing documents that were seized in a surprise inspection from the San Francisco headquarters of JUUL Labs -- America's largest seller of electronic cigarettes.Agents collected material related to JUUL's sales and marketing practices in a surprise inspection last Friday. The FDA tells ABC News the surprise inspection was part of ongoing efforts to prevent e-cigarette use among young people. In addition to Tuesday's raid of more than 1,000 documents pertaining to the company's marketing practices, the FDA has also cracked down on the company in the past with unannounced on-site inspections.At Jeet Big Times smoke shop on Polk Street in San Francisco, the JUUL is just one of the dozens of e-cigarette products, but number one in sales."I sell it every day. Three or four packages or more," says employee Bal K.C.In 18 months, JUUL has made a meteoric rise. Now, according to UCSF's "Canter for Tobacco Control, Research and Education," it's dominating 70 percent of the e-cigarette market."It became a high school and college phenomenon," says Pamela Ling, professor of medicine at UCSF."JUUL even admitted when they started out they were marketing to youth. They had Instagram accounts, did a lot of social media promotion -- they later admitted it was a mistake." says Ling.A high school student named Alonso outside of Mission High School says he sees ads for the device all over and knows his peers are using it."I smell it in the hallways," he said.While JUUL comes in a variety of flavors like other e-cigarette products, what sets JUUL apart is its small USB-like shape which is easily concealable in a setting like a school or at home. Its high concentration of nicotine is the equivalent of a pack of cigarettes per cartridge, giving users a faster head rush. Users are also drawn to the device's bright rainbow lights called "party mode," which is activated once the user takes a drag and waves the device back and forth."It doesn't have the stigma and on a sub-level, it's something you keep in your pocket," says Ling.A spokesperson for JUUL sent this statement, saying in part, the company is "committed to preventing underage use and want to engage with FDA, lawmakers, public health advocates and others to keep JUUL out of the hands of young people," adding they already "released 50,000 pages of document to the FDA since April."