Sinead O'Connor left for a bike ride in Wilmette, a Chicago suburb, 6 a.m. Sunday morning. She has not been seen since, according to police, who are now actively searching for the singer.
"A caller has expressed concern for her well-being, and no other information is available at this time," a statement from the Wilmette police said.
Detectives were tasked with finding the singer Sunday afternoon.
The singer has struggled with suicide attempts in her past. Her social media posts also hint at ongoing struggles, including her 12-year-old, Shane, being placed into family care in Ireland. O'Connor is also being sued for libel for comments regarding Arsenio Hall and the death of Prince.