VATICAN CITY • Happiness is not an app you can download on your mobile phone, Pope Francis told thousands of teenagers yesterday at a mass to mark a weekend dedicated to youth.

"Freedom is not always about doing what you want. In fact, it is the gift of being able to choose the right way," he said in a homily punctuated by regular bursts of applause from the crowd in a packed St Peter's Square.

"Your happiness has no price. It cannot be bought and sold. It is not an application you download on a mobile phone. Even the latest version cannot help you to grow and become free in love," the pontiff added.

An estimated 70,000 teenagers were in Rome for a weekend of events to celebrate Pope Francis' Jubilee Year dedicated to the theme of mercy.

In a surprise move last Saturday, the 79-year-old heard confessions from 16 of them and a video message from him was broadcast at a rock and rap concert in the Stadio Olimpico.

The importance of mobile phones to teenagers was also reflected in Francis' message at the concert. Clutching an iPhone, he told the audience that living without Jesus was like not having any signal. "Always be sure to go where there is a network: family, parish, school," he said.

AGENCE FRANCE-PRESSE