The 17-year-old has been detained for the past two weeks after being found in the home of a man - suspected of smuggling aspiring Isis fighters across the border - in the Mithatpasa quarter of the southern Turkish city of Adana, according to Italian media reports.
The girl, who has an Italian mother and Tunisian father, was travelling alone.
Italy's Ministry of Foreign Affairs confirmed that the girl, who lives in the outskirts of Paris, was being detained.
She has not been charged of any crime but it is suspected that she tried to follow a group foreigners who were staying in the same apartment before crossing the border. They included four French people, an Indonesian, a German, an Egyptian and a Saudi Arabian, according to the reports.
The city is a popular stopover for would-be Isis militants, with 75 people being intercepted so far this year by Turkish authorities.
Some 81 Italians have joined the ranks of Isis, according to the most recent figures.
The most high profile case is that of 28-year-old Maria Giulia Sergio, who left for Syria with her Albanian husband in September last year.
The Muslim convert, who changed her name to Fatima Az Zahara, gave a chilling interview over Skype to La Repubblica in July, in which she described the Islamic State as “the perfect country”.
By Ellie Bennett