The Holy Father called James Foley's Catholic parents to 'offer his condolences and promise his prayers.'
A video of Mr Foley's death was posted online by the extremist group I.S., formerly known as ISIS, on Wednesday.
The man who appears to have beheaded the journalist had an English accent and authorities in Britain are said to be analysing his voice to identify him.
On Facebook Mr Foley's mum Diane said: "He gave his life trying to expose the world to the suffering of the Syrian people.
"We implore the kidnappers to spare the lives of the remaining hostages. Like Jim, they are innocents. They have no control over American government policy in Iraq, Syria or anywhere in the world.
"We thank Jim for all the joy he gave us. He was an extraordinary son, brother, journalist and person. Please respect our privacy in the days ahead as we mourn and cherish Jim."
Another post on the Facebook page said: "Please be patient until we all have more information, and keep the Foleys in your thoughts and prayers."
Mr Foley's family are devout Catholics and their parish priest spent 45 minutes with them soon after his death was confirmed.
Fr Paul Gousse, of Our Lady of the Holy Rosary, left the house in Boston without speaking to reporters.