A 29-year-old dental student at Columbia University has been missing since April 1 when she walked out of her Manhattan apartment without telling her roommates where she was going.

Jiwon Lee was last seen around 9:30 p.m. that night. Shortly before vanishing, she called her brother, Matt Lee, a Columbia med student, and someone else whose number her friends didn't recognize, CBS News says.

Her cellphone signal was tracked to a tower on 179th Street near the George Washington Bridge, according to the Columbia Spectator.

Reports in the Daily News and Daily Mail said that Lee had attempted suicide days earlier.

Lee, who has depression and a bipolar disorder, according to the Daily News, left suicide notes that were found by New York Police Department investigators.

At Columbia, Lee became president of the American Student Dental Association. She also performed stand-up comedy in the city's clubs and appeared on Comedy Central's Open Mic Night.

Her family is raising money to hire a private investigator to look for her. By Wednesday afternoon, they'd received more than $70,000 in donations on their GoFundMe account.

Lee is 5-foot-2, 120 pounds and has black hair and black eyes.