The mother of an 18-year-old woman missing for more than 72 hours fought off tears as she made a public plea for her daughter's safe return Friday afternoon.

"Michelle, I know you are a good girl and I don't know what happened," Sharon Wu Yu told CP24 following a news conference outside York Mills Collegiate Institute, where her daughter is a student. "Do something to say you are safe. That's all I want."

Michelle Yu was last seen Tuesday at about 2:30 p.m. near York Mills Road and Chipstead Road and then at about 6 p.m. when she used her bank card at a TD Bank at 354 Bay St., south of Queen Street West, in downtown Toronto.

In an interview with CP24 on Thursday, Det. Const. Roger Marchack said Yu appears to have disappeared of her own free will, but on Friday Yu's mother said it's unlike her daughter to just disappear.

"She is a very normal girl," she told CP24 following the news conference. "She has tons of friends to talk to and she doesn't have any problems. Something is unusual."

Family and friends of Yu have been distributing posters featuring her photo throughout the city and have solicited information about her whereabouts using several social media sites.

On Thursday, Yu's Grade 12 classmates at York Mills Collegiate Institute attended an assembly where they discussed further ways to help locate the missing girl.

"We are very, very concerned and we want to hear from her," Principal Clara Williams told reporters. "We just want to hear that Michelle is safe and if she feels that she cannot come back right now, we want her to call any one of her friends and tell them that she is OK."

Michelle Yu is Asian, five-foot-seven and about 125 pounds with a slim build. She was wearing a grey hoodie, brown moccasins and eyeglasses when she was last seen.

Anyone with information about Yu's whereabouts is asked to call police at 416−808−3300 or Crime Stoppers anonymously at 416−222−TIPS (8477).