Father Paolo Dell'Oglio from Italy was kidnapped near the city of Raqqa last 29 July.
He had been an outspoken critic of the Assad government in Syria during the start of the civil war in the country.
It's not known who took the Jesuit priest and there has been no news on his location or condition.
Through the Vatican Information Service his family said: "One year has already passed since we last knew of our son and brother Paolo, priest, Jesuit, Italian, who disappeared in Syria on July 29th 2013.
"This has also been a long time, too long, for a land ravaged by war and infinite suffering like Syria.
"We ask those responsible for the disappearance of a good man, a man of faith, a man of peace, to have the dignity to let us know of his fate.
"One year after his disappearance, many of us will be praying for him and standing by him, as we will be doing for those who have been kidnapped, unjustly detained and for the many who are suffering because of this war."
Here's a video they posted on YouTube:
One of his friends, Dr Harry Hagopian told Premier's News Hour it's not clear if he is still alive: