In his address, the Pope urged the pilgrims not to be "part-time" Christians but to lead full, meaningful lives.
On his first overseas trip as pontiff, Francis also attended the Catholic World Youth Day.
Speaking from a huge stage at the four-km-long beach where a mock church structure was built, the Pope referred to street protests taking place in Brazil for more than a month against corruption, poor public services and the high cost of events like the 2014 World Cup.
"The young people in the street are the ones who want to be actors of change. Please don't let others be actors of change," he said.
"Keep overcoming apathy and offering a Christian response to the social and political concerns taking place in different parts of the world."
By the time the Pope's car had reached the stage, the back seat was filled with football shirts, flags and flowers thrown to him by pilgrims lining the route, the report said.
Almost every inch of the beach was occupied as most of the young people stayed on, pitching tents or sleeping in the open.
On Saturday, in a speech to 1,000 bishops and clerics in Rio's cathedral, the Pope said they should go to the shanty towns.
"We cannot keep ourselves shut up in parishes, in our communities, when so many people are waiting for the Gospel," he said.
--IANS (Posted on 28-07-2013)