He told a crowd of 50,000: "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."
As quoted by The Telegraph, "futile" behaviours young people should avoid include:
"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."
Pope Francis has 4.3m Twitter followers and accounts in several different languages.
