Two-thirds of adults contacting StepChange Debt Charity for help last year were aged under 40, its figures show.
Some 66% of people contacting StepChange in 2019 were aged 18 to 39, a proportion which has grown from 57% in 2014.
More than six in 10 (62%) people contacting the charity for help were women, an increase of five percentage points in the past five years.
Single parents made up a quarter (24%) of those who sought advice from StepChange in 2019, of whom 87% are women.
Overall, the charity contacted by 635,091 people in 2019.
Clients had an average of £14,129 in non-mortgage debt in 2019, an increase of 8% in the past three years.
Seven in 10 (69%) new StepChange clients had at least one credit card debt, with the average amount owed at £7,635.
Nearly half had at least one overdraft debt at the time of contacting the charity, owing nearly £1,500 on average.
The most common reasons for debt among new StepChange clients were reduced income (18% of new clients), unemployment or redundancy (16%) and injury or illness (16%).
The charity is urging anyone who is concerned about the impact of coronavirus on their finances to seek advice as soon as possible.
StepChange chief executive Phil Andrew said: “These figures tell us that financial resilience is already critically low, despite the fact that most of our clients come from in-work households.
“This should show policy makers during the current economic crisis how radical they will need to be to shore up UK families.”
He continued: “We would urge Government, creditors and employers to take all necessary steps to protect financially vulnerable people from falling further into difficulty and we stand ready to do all we can to continue to provide our services to people who need them.”