MOUNT PLEASANT, Mich. -

The FBI has joined the investigation into the disappearance of a 4-year-old boy from the Saginaw Chippewa Indian Tribe in mid-Michigan. Authorities say they've identified a "person of interest" in the case.

The Mount Pleasant Morning Sun reports Saginaw Chippewa Tribal Police released a statement early Saturday calling Carnell Chamberlain's disappearance "mysterious." The statement didn't say if authorities had spoken to the person of interest.

Tribal spokesman Frank Cloutier said in a statement late Friday afternoon that the search was ongoing in the Mount Pleasant area after Chamberlain was reported missing around 10 p.m. on Thursday. More than a dozen agencies were involved in the search.

Seventy-eight firefighters and more than 150 volunteers searched a 1-mile radius of where the boy last was seen, about 120 miles northwest of Detroit.