The Los Angeles County Sheriff's Department says Amanda Kathleen Custer, 31, was kidnapped Monday in the back of a gray Prius sedan, with California license place 8AOR167, in the 600 block of Vaquero Road, Monrovia.
The Prius was reported to have been last seen Monday morning traveling north on Padua Road in Claremont toward Mount Baldy, according to investigators.
Residents who live on Mount Baldy Road, Glendora Ridge Road and Glendora Mountain Road should stay alert for any signs of Custer, they added.
Homicide investigators are also looking into footage that was taken Monday night, the day before suspect Robert Anthony Camou was arrested after a four-hour standoff with police.
Video shows the 27-year-old dancing at a downtown Los Angeles bar during an open mic night, attempting to grab the microphone from the host.
Michael Moore, the man who shot the video, tells Eyewitness News that Camou was saying things about a woman he buried in the dirt.
Now, investigators are trying to determine if what Camou said in the video could have anything to do with Custer's disappearance.
"We are very concerned for her well-being. We're asking her, if she's OK, to please contact any law-enforcement officer," said Lt. Scott Hoglund of the Los Angeles County Sheriff's Department Homicide Bureau at a Tuesday press conference.
Authorities said Custer and Camou had been in a tumultuous dating relationship over the last two years, one marked by multiple allegations of domestic violence.
A restraining order filed by Custer in February included details of Camou's alleged obsessive behavior.
"He has made over 100 (phone) numbers to verbally bash me," Custer said in a court document at the time. She went on to describe an uninvited visit to her home by Camou: "He turned around, came running at my window, and broke my double-pane window with the hatchet."
Camou remains in police custody without bail on unrelated burglary and domestic violence charges.
A vigil was held Wednesday night for Custer.
"We're just asking all of the community, when you're out there, you're hiking, you're doing things, keep your eyes open," said Monrovia resident Carmen Martinez. "We're looking for a miracle."
Anyone with information is asked to call the Los Angeles County Sheriff's Department Homicide Bureau at (323) 890-5500. Anonymous information can be provided to Crime Stoppers at (800) 222-TIPS.