Addressing faithful in St Peter's Square, the pontiff also called for the release of all hostages in conflict zones around the world.
He said: "Dear brothers and sisters, in the hope given to us by the risen Christ, I renew my appeal for the release of all hostages in zones of armed conflict.
"In particular I would like to recall the Salesian priest Tom Uzhunnalil, kidnapped in Aden in Yemen on March 4."
Gunmen stormed a care home run by nuns in the Yemeni capital Aden in March, murdering four nuns and 12 elderly people.
Their identity has not been confirmed but it is believed they are Islamist terrorists aligned with Islamic State.
The militants then kidnapped Fr Tom Uzhunnalil, a priest who was in the care home's chapel during the attack.
