POPE Benedict XVI has told 1.5 million pilgrims in Madrid not to seek faith without the Church, warning they risked following a "counterfeit Jesus".

"Make Christ, the son of God, the centre of your life," the 84-year-old told a sea of young Roman Catholics gathered at an airbase for a mass culminating World Youth Day celebrations.

"Let me also remind you that following Jesus in faith means walking at his side in the communion of the Church," he cautioned.

The leader of the world's 1.5 billion Roman Catholics was alluding to "pick and choose" believers who follow only some precepts of the Church while dispensing with others that are harder to accept.

"We cannot follow Jesus on our own," the pope said.

"Anyone who would be tempted to so do 'on his own' or to approach the life of faith with the kind of individualism so prevalent today will risk never truly encountering Jesus, or will end up following a counterfeit Jesus."

The pope called on the pilgrims to join in the lives of their parishes, communities and religious movements, as well as the celebration of Sunday mass, frequent confession, and prayer.

"Do not keep Christ to yourselves," the pope told the pilgrims from 193 nations.

"Share with others the joy of your faith," he said, urging them to bear witness to their faith even where they are met with "rejection or indifference".

The pilgrims were from countries "filled with young people who are looking for something greater and, because their heart tells them that more authentic values do exist, they do not let themselves be seduced by the empty promise of a lifestyle that has no room for God," the pope said.