Jennifer Graves-Smith walked away from Halifax West High School on Tuesday afternoon. (Halifax Regional Police)Halifax police are asking for the public's help finding an 18-year-old with autism who didn't show up for her bus ride home from school Tuesday afternoon.

Jennifer Graves-Smith was last seen leaving Halifax West High School at about 3:30 p.m. She is a special-needs student and was reported missing when she did not take her assigned bus home.

Staff Sgt. Darrell Gaudet of Halifax police said in a release that someone saw Graves-Smith walking on a wooded pathway toward Keshen Goodman Public Library on Lacewood Drive, and she has not been seen since.

She is described as white, about five feet eight inches tall and 130 pounds, with shoulder-length brown hair. Graves-Smith was last seen wearing a blue Columbia Sportswear jacket and carrying a red and black backpack. She would likely have the hood on her jacket pulled over her head, police said.

"The thing with her is basically … if she is approached by people, a lot of times she will turn away," said Gaudet. "That is a concern for us too as we're out here looking for her."

Police handed out flyers Tuesday with Graves-Smith's picture in the Clayton Park and Bayers Lake communities. Halifax Regional Search and Rescue were also called to assist in the search because of the terrain.

Halifax Regional Search and Rescue members look for Jennifer Graves-Smith on Tuesday. (CBC)Many of the searchers were bundled with scarves and hats in an effort to keep out the freezing temperatures, which dipped to at least –20 C.

"Basically this is out of her normal pattern. She does miss her bus the odd time, but she will return home a short time later. So this is out of her normal pattern," said Gaudet.

Police do not believe the teen has been the victim of foul play.

Anyone with information is asked to contact Halifax Regional Police.