SAN FRANCISCO — The leaders of a small start-up, PAX Labs, gathered at a board meeting in early 2015 to review the marketing strategy for its sleek new electronic cigarette, called Juul. They watched video clips of hip young people, posed flirtatiously holding Juuls. And they talked about the name of the gadget, meant to suggest an object of beauty and to catch on as a verb — as in “to Juul.”

While the campaign wasn’t targeted specifically at teenagers, a former senior manager said that he and others in the company were well aware it could appeal to them. After Juuls went on sale in June 2015, he said, the company quickly realized that teenagers were, in fact, using them because they posted images of themselves vaping Juuls on social media.

The former manager said the company was careful to make sure the models in its original campaign were at least 21, but it wasn’t until late 2016 or January 2017 that the company said it decided the models in all Juul ads should be over age 35 — to be “better aligned” with a mission of focusing on adult smokers. Only in June of this year did the company again change its policy, this time to using only real people who had switched from cigarettes to Juul.

The company recently modified the names of its flavors — using creme instead of crème brûlée and cucumber instead of cool cucumber. Juul said it “heard the criticism” that teenagers might be attracted to the flavors and “responded by simplifying the names and losing the descriptors.”