Trinity Homeless Project launched The Big SleepOut, at Bar Italia, on Thursday (May 14).
The Big SleepOut will see 1,000 people sleeping in boxes on December 4 this year, in the hope of raising £200,000 to beat homelessness.
They will eat together, see live performers, hear from inspiring people and then bed down on a winter night in Hillingdon Athletics Stadium.
Uxbridge & South Ruislip MP Mr Johnson said he looks forward to further supporting Trinity in their work.
“Homelessness as an issue is getting more and more urgent," he said. "It takes love and commitment to help the homeless.”
“It could indeed be any one of us.”
Trinity believe that it takes the whole community to beat homelessness, so are asking people to join the London Mayor in their #ItCouldBeMe photo campaign.
It aims to raise awareness that homelessness can happen to anyone and so it is all of our responsibility as a community.
The Big SleepOut, which will see participants bed down for a cold, tough night of rough sleeping, has been held annually for six years in partnership with Slough Homeless Our Concern (SHOC).
Steve Hedley, Trinty CEO, said: “Trinity and SHOC feed and house well over 200 local people every year who suffer homelessness - assisting people to leave the streets, leave behind a life dominated by problems and to beat homelessness through achieving independence.
“The Big SleepOut is an opportunity for us all to walk in someone else's shoes - What we learn about ourselves and others through this invaluable experience.”
You can sign up now for seventh Big SleepOut online. Look out for #ItCouldBeMe on social media.