Pope Francis
© Tony Gentile / ReutersScarves are thrown to Pope Francis at the end of a mass for the Youth Jubilee in Saint Peter's Square at the Vatican, April 24, 2016.
Happiness can't be downloaded like a cellphone app, Pope Francis has said in a special mass for the teens in the Vatican on Sunday.

"Happiness has no price," the Pontiff said, adding that it's "not an app that you can download on your phones, nor will the latest update bring you freedom and grandeur in love," AP reported.

On Saturday, the head of the Catholic Church has made a surprise appearance before tens of thousands of youths gathered at St Peter's Square for a Holy Year weekend for teenagers.

Despite no earlier arrangements made, Pope Francis heard confessions from 16 youths, aged from 13 to 16 years.

The teens "appeared relaxed" as they unburdened themselves in front of the head of the Catholic Church, according to AFP.

The Pope spent over an hour at the square before warmly shaking hands with the youths, who confessed to him, and departing with a cheery "ciao, ragazzi!" (Bye, guys!).

A total of 150 priests heard confessions from thousands of teens at Vatican's main square as part of Francis's Jubilee year event.

The youths then passed through the so-called "Holy Door" in a basilica, with a ritual entitling to special indulgences during jubilees, which began in December and runs until November.

For the current jubilee one, which is the first one since 2000, the Pope has authorized priests to absolve women who have had abortions.

After religious ceremonies in the Vatican, the teens were entertained by a concert of rock and rap artists at the Stadio Olimpico in Rome.

In a video address broadcasted at the arena, Pope Francis also compared being out of contact with God through lack of love to being in an area with no cellphone reception in an attempt to connect with the younger audience.