Maelys de Araujo was last seen in the early hours of Sunday at the community hall in the village of Pont-de- Beauvoisin, about 50 kilometres north of Grenoble, where the wedding was held.
Scores of police, search and rescue teams, divers and cavers have spent the week trawling through the heavily wooded area for signs of her.
Investigators suspect that the little girl with dark brown hair and eyes, who was attending the wedding with her parents, was kidnapped.
The man is a friend of the 34-year-old wedding guest arrested on Thursday, also over inconsistencies in his story.
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Baudoin said the man taken into custody on Thursday was absent from the wedding during a period that could correspond with Maelys's disappearance.
A source close to the investigation said the police were looking into a mobile phone that he concealed from the authorities.
The police will compare his account of events with that of his friend, Baudoin said in a statement.
While the case is being treated as a kidnapping, Baudoin said Friday that no line of investigation was being ruled out.
Sniffer dogs lost the scent from Maelys's cuddly toy in a car park outside the venue, raising fears she was kidnapped and whisked away by car.
A gendarme squad from the Paris region arrived Wednesday to assist in the search.
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