VATICAN CITY (AP) -- Pope Leo XIV surprised tens of thousands of young Catholics on Tuesday and showed up unexpectedly at a Holy Year welcome ceremony, thrilling the kids and receiving a rock star's welcome in the first big youth event of his pontificate.

Leo emerged in St. Peter's Square in his popemobile at the end of an evening Mass that kicked off the Jubilee of Youth, a weeklong celebration for young Catholics. The estimated 120,000 young pilgrims who had packed the square erupted in shocked cheers and chants, as Leo looped around the square and up and down the boulevard leading to it.

For 20 minutes, Leo beamed, waved and clearly seemed to enjoy the outpouring of enthusiasm from his perch on the popemobile, as he took in the sea of cheering, flag-waving young people from around the world as the setting sun cast a golden glow over the basilica.

In a brief off-the-cuff salute and blessing from the altar, he told the young pilgrims that they were beacons of light, hope and peace that the world needs today.

"The world needs messages of hope. You are this message, and must give hope to everyone," he said in a mix of Spanish, English and Italian. "We want peace in the world. We want peace in the world!"

Leo, the first American pope, hadn't been expected to meet with the young pilgrims as a group until the weekend, when he was to preside over a vigil Saturday and Mass on Sunday in the highlight of the Jubilee week.

Tuesday's Mass had been celebrated by the Italian archbishop who organized the Holy Year, Archbishop Rino Fisichella, but it was he who urged the kids to not leave the square at the end, because the pope "had a surprise for us."

The crowd responded with the classic refrain from Catholic youth gatherings: "This is the youth of the pope."

This week, downtown Rome has swarmed with energetic, singing and dancing masses of teenage Catholic scouts, church and Catholic school groups whose numbers are expected to swell to 500,000 by the weekend.

It all had the vibe of a scaled-down World Youth Day, the once-every-three-year Catholic Woodstock festival that was inaugurated by St. John Paul II and maintained by every pope since.

Tuesday began with groups of Catholic influencers -- priests, nuns and ordinary faithful who use their social media presence to preach and teach the faith -- passing through the basilica's Holy Door, a rite of passage for the estimated 32 million people participating in the Vatican's 2025 Holy Year celebrations.

Francis met with some of the influencers earlier Tuesday and thanked them for using their digital platforms to spread the faith. But he warned them against neglecting human relationships in their pursuit of clicks and followers, and cautioned them to not fall prey to fake news and the "frivolity" of online encounters.

"It is not simply a matter of generating content, but of creating an encounter between hearts," Leo said in a speech that showed his ease in switching between languages. "Be agents of communion, capable of breaking down the logic of division and polarization, of individualism and egocentrism."

"It is up to us -- to each one of you -- to ensure that this culture remains human," he said. "Our mission -- your mission -- is to nurture a culture of Christian humanism, and to do so together" in what he called the only networks that really matter: of friendship, love and the "network of God."

Pablo Licheri, who founded the Catholic Mass Times app, which provides locations and times for Catholic liturgies around the world and has registered 2 million downloads, said that he has been heartened by both Leo's message of unity and the enthusiasm of young Catholics like him who have descended on Rome.

"I was especially moved to meet so many fellow Catholic influencers in person and to pray together with others who share the same passion for spreading the joy of God's love," he said after Tuesday's Mass.

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