He admitted it had proved more difficult than he expected to persuade people to sleep out overnight to raise awareness of homelessness.
But the award-winning social entrepreneur said he was already working on ideas for a “new and different” event to launch next year.
More than 8000 people who braved sub-zero temperatures in Princes Street Gardens in Edinburgh last year raised a total of more than £4 million for several initiatives aimed at tacking homelessness.
Mr Littlejohn said nearly 10,000 people will be raising around £3.2 million at mass sleep-outs in Edinburgh, Dundee, Glasgow and Aberdeen tonight. But he admitted planning this year’s event, which will see Scottish singers KT Tunstall and Amy MacDonald travel by helicopter to perform in all four locations, had involved “four times the work” of last year’s fundraiser.
Mr Littlejohn – who has won the backing of George Clooney, Leonardo di Caprio and Prince Harry for his Social Bite chain of sandwich shops and cafes – said he was “relieved” so many people had signed up to take part in the second Sleep in the Park event.
All participants must pledge to raise at least £100 to secure a place at the event, with corporate teams being asked to pay a minimum of £3000.
The top fundraisers receive a personalised Christmas hamper from First Minister Nicola Sturgeon and the chance to meet Nobel Peace Prize winner Malala Yousafzai at a gala Sleep Out “thank you” dinner in March.
When the expanded event was announced in the summer, Mr Littlejohn said he had hoped to sign up 12,000 people and raise at least £6 million as part of a drive to “eradicate” homelessness in Scotland within five years.
Mr Littlejohn said: “It’s a really difficult event to do two years in a row.
“A lot of people who did it last year viewed it as a once in a lifetime experience. It is a lot of effort for people to raise money from their friends and families, and everything else that is entailed with it.
“I’m really delighted to get to the level of participation and fundraising that we have.
“It could have gone the other way. We could have really struggled. I’m relieved and very grateful to everyone that has signed up and got behind it.”
Around 4000 people will take part in the Edinburgh event, which will be staged in Princes Street Gardens again, where Lulu, Admiral Fallow, Siobhan Wilson and Martha Ffion will be performing.
Mr Littlejohn added: “It’s definitely been more of a challenge this year but it was definitely the right thing to do to spread it geographically.
“If we’d just done it in Edinburgh, we’d have got a significant reduction in participation.
“We’ve not just done another event for the sake of it. We had a target to raise £1.5 million this year to put towards our ‘Housing First’ programme to lift more than 800 rough sleepers out of homelessness across Scotland.”