The phenomenon has infuriated relatives of those killed by Provenzano and Salvatore "Toto" Riina, the Italian news agency ANSA reported.
Maria Falcone's brother, Giovanni, was a magistrate assassinated in 1992, a killing ordered by Provenzano and Riina.
''Unfortunately, evil still fascinates our young people," she told Repubblica. "Certain messages on the Internet and certain films are not helping.''
Riina, serving 12 life sentences, has been imprisoned since 1993. Provenzano, also a native of Corleone in Sicily, succeeded him as the Mafia "super boss" and was arrested in 2006 on the sheep farm where he was hiding.
Riina's Facebook fan club site has more than 2,000 subscribers. They have posted Christmas messages that tell him he is "great."
Provenzano has one site with 202 subscribers who celebrate his 40 years in hiding. Another site with a smaller membership calls for his canonization.