The sister of Markham woman who was last seen on Tuesday implored her to call home as a comprehensive four-day police search has failed to turn up any clues.

York Regional Police say an extensive air and ground search of wooded areas, waterways and other open spaces in Markham has yielded no new clues as to the whereabouts of the 23-year-old.

Sandy Luong was last seen leaving her home near the intersection of Helen Avenue and Kennedy Road at about 2:30 p.m.

Tracy Luong, says she was staying with her father for the last month. She said her sister only said she was going outside for a walk before leaving the home on Tuesday.

“It’s not like her to be gone for this long,” Tracy Luong said.

Tracy said her sister is very soft spoken and kind.

“If she only had one dollar she’d rather give it to someone else to help them,” her sister said.

Police have even called in their helicopter and drone to search for Luong, but haven’t had any luck so far.

Searchers were on the grounds of Unionvillle Meadowvale Public School on Friday morning.

Const. Nate Matthew said it is possible Luong has some bus tokens, but does not have her ID or money with her.

“Sandy, if you hear us, we just want to know you’re safe,” Tracy Luong said. “If you could just call anyone, we just want to know you’re okay.”

Tracy Luong said the family used to live in the East York area of Toronto, and Sandy also lived in the area of St. Clair Avenue West and Caledonia Road, so she is familiar with many parts of Toronto as well as the TTC system.

Police want homeowners in the area to search their properties, including sheds and garages.

Luong is described as an Asian woman, standing five-feet-five inches tall, weighing 100 pounds. She has short black hair with bangs.

She was last seen wearing a long purple winter coat, a black skirt and black boots.

Anyone with information is asked to call police at 1-866-876-5423, ext. 7541, or Crime Stoppers at 1-800-222-8477 (TIPS).