The pontiff has over 14 million followers across his nine Twitter accounts, tweeting in different languages, compared to the 43.7 million social media users following Obama.
The most used words on the Pope's Twitter accounts are God, Jesus and love, according to the Twiplomacy study.
The pontiff's most popular tweet – attracting more than 39,000 retweets – was sent on Easter Sunday earlier this year, when the Pope declared: "Christ is risen! Alleluia!"
Christ is risen! Alleluia!
— Pope Francis (@Pontifex) April 20, 2014
The Italian premier has a much lower profile on Twitter; with just over a million followers Renzi comes in 26th place in the study of most followed world leaders.
The account of the UK prime minister's office has more than twice as many followers as Renzi, giving David Cameron a stronger online presence and ranking 13th in the world.
Renzi can, however, boast at being more popular than French President Francois Hollande, who counts just 648,000 Twitter followers.
The centre-left prime minister's most popular tweet was a jibe against disgraced leader Silvio Berlusconi, sent on December 10th 2012 and attracting over 9,300 retweets.
"Dear Silvio, you can buy things, but you cannot buy people. Not all of them, at least. And certainly not me. You have opened the doors for me? Close them, it's getting cold! #ciao," Renzi wrote.
Caro Silvio, le cose si possono comprare, le persone no. Non tutte, almeno. Io no. Hai le porte aperte per me? Chiudi pure, fa freddo! #ciao
— Matteo Renzi (@matteorenzi) December 10, 2012
Despite being behind other leaders internationally, Renzi has a greater social media presence than Italy's former prime ministers.
His predecessor, Enrico Letta, has just 343,000 followers, while Mario Monti, who was prime minister from November 2011 to April 2013, currently has 279,000 followers.