Police and volunteers have spread out across Toronto to search for a PhD student who’s been missing for the past four days.

The York Regional Police Service says Zabia Afzal, 30, was last seen Thursday morning in the area of Ashbridges Bay, a park in the east end of Toronto along the shores of Lake Ontario.

Over the weekend, about 70 volunteers have placed roughly 7,000 posters across the city. Search crews have been focusing their efforts on various parks in the city.

“We’re not too sure why she is missing,” Zubair Afzal, Zabia’s brother, told reporters on Sunday. “Our goal at this moment is to find her and we’re asking everyone’s support for that.”

York Regional Police have used a helicopter to search from the air, while officers in Toronto are searching from the ground. Nearby bodies of water are also being searched.

Afzal, a Vaughan resident and a public health PhD student at York University, is described as a strong advocate for women’s rights.

“She’s the most brilliant person I know,” one of Afzal’s classmates told CP24. “She uses her brilliance for the good of the society that we live in. She is deeply moved by injustices big and small.”

Afzal is described as five-foot-four with shoulder-length, dark-brown hair. She was last seen wearing black pants, a black hoodie and a green floral shirt.

Anyone with information on Afzal’s whereabouts is asked to contact York Regional Police or Crime Stoppers.

With files from CP24