The 78-year-old pontiff delivered his message in a sermon to priests and nuns in the centuries-old Manila Cathedral, on the first full day of a trip to the Catholic Church's Asian stronghold.
The pope asked them to counsel young people, who may be confused and despondent living in a corrupt society, on traditional values.
"Proclaim the beauty and truth of the Christian message to a society which is tempted by confusing presentations of sexuality, marriage and the family," Francis said.
His comments come amid a struggle in the Philippine Catholic Church between a conservative hierarchy and many followers living lives more in line with some modern Western values.
Aside from the Vatican itself, the Philippines is the only state in the world where divorce is illegal, while abortion and same-sex unions are also banned.
However the Church in 2012 lost a 15-year battle on birth control, as Congress passed a law allowing the state to hand out free contraceptives and teach family planning at schools.
Francis received a rapturous welcome when he arrived in the Philippines yesterday for a five-day visit that is part of the Catholic Church's drive to attract more followers in Asia.
The Philippines is the Church's bastion in Asia, with Catholics making up 80 per cent of the former Spanish colony's 100 million people.
