DETROIT (AP) — Police went door to door Wednesday to publicize the search for a 13-year-old Detroit girl who has been missing since riding a school bus in early January.

“We’re hopeful that we find her well, but we can’t operate on hope,” Detroit Police Chief James White said.

Na’Ziyah Harris was last seen departing a bus Jan. 9. Police don’t believe her disappearance started as an abduction. Few details about the investigation have been released.

White said his department has taken over the case from the school district’s public safety department.

“We were very, very concerned,” he said after being briefed by the district. “We’ll be bringing in our local, federal, state partners.”

Deputy Chief Kari Sloan described the search as an aggressive one and said all witnesses were being interviewed again.

“She’s been missing for a very long time,” grandmother Anette Harris told reporters. “Na’Ziyah is a very sweet child. This is not of her character. ... I can’t sleep. I can’t eat. Just bring her home, please.”