"Maybe many young people waste too many hours on futile things," the pope said in a short speech to the altar servers - young people who help the priest during religious services - who had come to Rome on a pilgrimage.
"Our life is made up of time, and time is a gift from God, so it is important that it be used in good and fruitful actions."
Activities cited by Francis as futile were: "chatting on the Internet or with smartphones, watching TV soap operas, and (using) the products of technological progress, which should simplify and improve the quality of life, but distract attention away from what is really important."
The 77-year-old pope has Twitter accounts in several languages. They were first used by his predecessor Benedict in 2011, and his English language account has 4.3 million followers.
He has described the Internet as a "gift from God", but also cautioned that high-speed world of digital social media needed calm, reflection and tenderness if it was to be "a network not of wires but of people".
In April, the Vatican began engaging pilgrims via social media for the canonisation of John Paul II, the Polish pope who attained rock star status by the time he died in 2005. Besides the www.2papisanti.org official website, the Vatican had set up several Facebook pages using the "2popesaints" theme, as well as accounts on Twitter (@2popesaints), YouTube (2popesaints) and Instagram (#2popesaints).
Written with agency inputs
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