The Jesuit priest was kidnapped by Islamic State militants on 29 July 2013 in Raqqa.
On the anniversary of his disappearance, a friend of his Fr Fadi Daou has told Premier he still holds a hope that he is still alive but believes he has probably been killed.
Fr Fadi, who runs the interfaith organisation Adyan Foundation, said: "We don't have other information from that time, for two years now.
"We know that ISIS are crazy men and it is totally possible that they have killed him.
Father Paulo was a controversial figure in Syria because of his humanitarian work. He was expelled from the country the year before his kidnapping for helping victims of President Bashar al-Assad's military crackdown.
His disappearance came after two bishops were kidnapped on the Turkish border. Their whereabouts are also unknown.
Fr Fadi's calling on Christians to keep the men, and others who've gone missing, in their prayers.
"We have the bishops of Allepo and also peace builders, Christians and Muslims who have disappeared in Syria," he said
"We have to, every day, pray and hope that they are safe.
Pope Francis made an appeal last week for the international community to do more to secure the release of the clergymen. Hetold crowds in St Peter's Square he wanted "a renewed commitment" from Syrian and international authorities, "so these brothers of ours can regain their freedom soon".
A call to not forget the men has also been made by Nigel Baker, the UK ambassador to the Vatican. Writing on his blog, he said: "It is right that we do not forget. And we should continue to use every opportunity to call for the release of the kidnapped, alongside all others of any faith held captive in Syria because of who they are, what they believe and what they do.
"It is their example of dedication to the other, not that of the extremists, which will build the new Syria from the ashes of the old."
The UK Government has also called for the release of Fr Paolo. Foreign Office Minister Tobias Ellwood tweeted that all people imprisoned for their faith or belief should be released.
2 years today since Fr. Paulo Dall'Oglio kidnapped in Syria. UK calls for his release & that of all imprisoned in Syria for faith or belief— Tobias Ellwood MP (@Tobias_Ellwood) July 29, 2015
Listen to Fr Fadi speaking on MENA Analysis (the show broadcasts on Thursday 30 July at 10pm):