He said London was committed to ensuring a sporting legacy from the Games – and to providing thousands of jobs and homes.
The Mayor also said crime had dropped in London by about 5% during the 16-day sporting festival.
Mr Johnson thanked those involved in delivering the games, including volunteers, security and transport staff.
Mr Johnson told a press conference in London: “There are a series of exciting global sporting competitions (coming to London) and it is in that context we want to be expanding very vigorously now the number of young people who take part, we want people of all ages to take part in sport.
“We have seen 3,500 applications for people to get involved in sporting activities since the Games began. Kate Hoey, the commissioner for sport, will obviously be taking that forward very actively indeed.”
And Mr Johnson reminded people that the Games were not over, with the Paralympic Games due to start shortly.
He urged sports fans to look for tickets amid “massive demand” in the wake of the events of the past fortnight.
And the mayor said: “The best way to make sure you have a chance to get to that park, share in the excitement of London 2012, is to get on the website when those Paralympic Games tickets become available.
“If demand exceeds supply, we will make sure there are Paralympic Park tickets available as well.”
The mayor said there were plans for 8,000 permanent jobs on the Olympic Park after the Games, and 8,000 new homes on top of the 2,800 in the Olympic Village.
Mr Johnson continued: “The Olympic task of thanking people now begins… I want to thank from the city’s point of view, the police, the Army, the armed services, who did such a wonderful job… I want to thank the men and women of G4S who worked fantastically hard and helped us deliver very, very safe venues indeed.
“The volunteers, I want to thank again the Team London volunteers, the Locog ambassadors, the TfL (Transport for London) ambassadors, and by the way I want to thank everybody in TfL high and low for an outstanding performance.
“Finally, I want to thank the people of London themselves, particularly because I think it was Londoners’ patience and kindness and imagination and enthusiasm that really got the whole thing going and helped us to deliver a great Olympics.”
Mr Johnson said the early indications were that London had already benefited economically from the Games and repeated hopes that the gains could ultimately reach £13 billion or more.