The prime minister met young people at Birmingham City's football ground
The government is pledging a further 85,000 "opportunities" to help get young people into work.
The scheme aims to help 45,000 young people to find jobs in retail, tourism, leisure and hospitality.
And it includes a pledge by retailer Morrisons to give extra training to all its 36,000 employees who are under 25.
But the Tories questioned how many people who were not already in work would be helped. The Lib Dems said it was "timid" and "lacking ambition".
Announcing the campaign in Birmingham earlier, Prime Minister Gordon Brown said that in the last recession, many young people found themselves out of work for months, or more than a year.
"We are determined that this does not happen again," he said. "For the first time, we are sitting here talking about the jobs of the future."
Backed by employers
A further 5,000 opportunities, including apprenticeships with companies such as Centrica, Carillion and Royal Mail, will also be created.
About 935,000 young people in England are not in employment or training, the last set of official figures showed.
Theresa May, for the Conservatives, questioned how many of them would be helped by the latest announcement and urged the prime minister to "come clean on the numbers".
"How many of these job and training opportunities are being offered to unemployed young people and how many are being offered to those already in work?" she said.
"We need to move beyond the era of spin and manipulation of figures which has had such a corrosive effect on public trust."
Liberal Democrat frontbencher Steve Webb said the plan would help "only a tenth of the young people who are unemployed today" and were "characteristically timid and lacking in ambition".
And while the plans were praised by the TUC general secretary Brendan Barber as "fantastic news", Bob Crow, head of the Rail, Maritime and Transport Union, said: "There's no point slashing real jobs in important sectors like transport and then massaging the unemployment figures with cheapskate, low-paid projects that are aimed at benefiting the bosses and letting the politicians off the hook."
The Backing Young Britain campaign will see £1bn spent to create 100,000 new jobs for young people and a further 50,000 jobs in what it calls "unemployment hotspots".
"We have both a moral obligation and an economic need to make sure that young people involuntarily without jobs aren't lost to work," Business Secretary Lord Mandelson told the BBC.
He said that the campaign meant the government would help companies train young people and include mentoring and internships, depending on the age.
But its success depended on the private sector, Lord Mandelson added.
"The government cannot deliver these opportunities by itself," he said.
More than 150 employers, including Microsoft and Pfizer, are said to be supporting the campaign.