Tens of thousands of young people told councils they were either homeless or at risk of becoming homeless over the past year.
Figures from 234 councils obtained through FoI showed some 45,000 18 to 24-year-olds made such an approach to their local authority.
But with more than 100 councils not providing information, the real statistic is pitched at over 70,000.
The Liberal Democrats carried out the research and leader Vince Cable said the statistics exposed a “national scandal”.
“These figures reveal the hidden homelessness crisis affecting young people, with an estimated 70,000 18 to 24-year-olds across the country turning to councils for help.
“The situation is being made worse by the government’s heartless decision to strip young people of housing benefit,” he said.
Charities cite the government’s decision to keep housing benefit frozen has exacerbated the problem – with gaps between funds and rent levels growing.
There are real fears that any block on single 18 to 21-year-olds receiving help with housing costs – unless they can prove they are particularly vulnerable – within Universal Credit will make the issue much worse.
Jean Templeton, the chief executive of St Basils, said the benefit change had left many young claimants facing an “impossible situation”.
“On the underlying presumption they are not entitled to support with housing costs they are unlikely to receive an offer of accommodation – as landlords who have several tenancy options presume their rent is at risk”, said Templeton.
“But without an offer, people cannot apply for housing support nor the necessary exemption if they are aged between 18 and 21”, she said, warning that this placed more young people at risk of rough sleeping and unsafe housing options.
The figures show that many more young people are turning up at their local council to warn of a risk of homelessness than are actually being accepted as in need of urgent support.
Of the 45,000 presenting as at risk of losing their home in the year up to September 2017, only 10,000 were classified as statutory homeless.
The data shows the highest numbers were in Bradford (1,828), followed by Manchester (1,297), Cornwall (1,127), Nottingham (1,091) and then Telford and Wrekin (1,051).
Manchester City Council said homelessness was a national problem “being stoked by welfare changes and the ongoing impact of austerity” and said young people were far from immune.
It said the government had dismantled safety nets that used to exist, but insisted it was working hard to tackle the issue, including through prevention.
Paul Noblet of Centrepoint said the most alarming thing about the figures was that they were likely to be a serious underestimate.
“As a country, if we want to break the cycle of homelessness we need to be honest about the scale of the problem and decide if we are serious about solving it,” he said.
Responding, the government stressed councils had a duty to help those most in need of temporary accommodation with £24bn a year being spent on help with housing costs and over £1bn up to 2020 to reduce all forms of homelessness.
The response also referenced investment in the Fair Chance Programme to support 18 to 25-year-olds with specific needs to help them find suitable accommodation.