A person in the audience wears a shirt against JUUL as JUUL Labs co-founder and Chief Product Officer James Monsees, foreground, testifies before a House Oversight and Government Reform subcommittee on Capitol Hill in Washington, Thursday, July 25, 2019, during a hearing on the youth nicotine epidemic.

"We would not be where we are as a company today without the extraordinary efforts of a few individuals who have asked to transition out of the company. I want to make sure to specifically thank each of them," Crosthwaite, a former Altria executive, said in an email sent to employees Monday.

Several top executives have left the company, including Chief Administrative Officer Ashley Gould and Chief Financial Officer Tim Danaher, two veteran employees at the young start-up. Newcomers Craig Brommers, chief marketing officer, and David Foster, senior vice president of advanced technologies, are also gone.

Juul CEO K.C. Crosthwaite has replaced the company's chief financial officer amid a management shake-up at the embattled e-cigarette maker, according to people familiar with the matter.

Juul appointed Guy Cartwright as its new CFO, a Juul spokesman confirmed to CNBC. Cartwright joined the company in July as transformation and operations officer, according to his LinkedIn profile.

"Over the past 3 months, Guy has been instrumental in helping us define our financial priorities and identify opportunities for efficiency," a company spokesman said in a statement.

Juul has eliminated the chief marketing officer position, according to the spokesman. It was not immediately clear whether Juul would fill Gould's and Foster's positions. Co-founders James Monsees and Adam Bowen, who formerly held the positions of chief product officer and chief technology officer, respectively, will join a newly formed founders office, where they will advise Crosthwaite.

The changes were announced in the email sent to employees. They come as Juul prepares to cut about 500 jobs, or about 10% to 15% of its total head count, by the end of the year. Before the cuts, Juul boasted about 4,100 employees.

"As the vapor category undergoes a necessary reset, this reorganization will help JUUL Labs focus on reducing underage use, investing in scientific research, and creating new technologies while earning a license to operate in the U.S. and around the world," Crosthwaite said in a separate statement addressing the layoffs Monday.

The shake-up comes just a month into Crosthwaite's tenure. The longtime Altria executive succeeded former Juul CEO Kevin Burns, who steered the company through its deal with Altria. The tobacco giant invested $12.8 billion in Juul in December.

The deal sent Juul's valuation soaring to $38 billion. It prompted intense criticism from public health advocates who said taking money from the top U.S. cigarette manufacturer undermines Juul's stated mission to help eliminate smoking.

The situation has quickly worsened for Juul in the nearly year since announcing the deal. At least one hedge fund has reportedly slashed the value of its stake in Juul to a price that values the e-cigarette maker at $24 billion.