WOODSTOCK, Ont. - Police, fire crews and volunteers have scoured this southwestern Ontario city around the clock for any sign of a missing eight-year-old girl, but after more than four days police announced Monday their ground search for Victoria Stafford has been completed.

They say they are still hopeful the girl, known to friends and family as Tori, is still alive.

The pretty, blond Grade 3 student vanished after school on Wednesday and police have been looking for her since that evening. The only tangible lead police have discussed publicly is surveillance video from around the time Tori disappeared showing her walking with an unidentified woman.

Oxford Community Police have referred to the woman as a "person of interest" rather than a suspect, and have not called Tori's disappearance an abduction.

"Every indication tells us, everyone believes this too, that Tori willingly walked away with an unidentified female," Const. Laurie-Anne Maitland said Monday.

The ground search was largely confined to the city of Woodstock itself, suggesting police believed she had not left her hometown. Crews searched numerous lakes, ponds, wooded areas, brushes and properties but found nothing relevant, Maitland said.

The investigation is still active and police officers could be seen canvassing neighbourhoods door-to-door Monday afternoon.

Behavioural sciences officers with the Ontario Provincial Police were brought in Sunday for a full day of consultations, Maitland said. She said she is heartened that police have not found evidence of foul play.

"When we're actively doing a grid search, we're not looking for necessarily a happy, healthy eight-year-old," Maitland said.

"When we're doing the ground search, every time I hear there's no news, that's a good thing."

Tori's smiling face adorns hundreds of flyers plastered all over the city, from telephone poles, to homes and businesses and even on many car windows. But despite national media coverage, intense attention from the public and more than 300 tips phoned into police, investigators still do not know who the woman on the surveillance video is or why she was with Tori.

Tori's parents, aunts and uncles have each watched the video hundreds of times, hoping to pick up on something, but no one in the large family says they recognize the woman with long, brown hair and wearing a white puffy jacket. Police say she is 19 to 25 years old, about five-foot-one or five-foot-two and between 120 and 125 pounds.

The Stafford family says they believe the girl will be all right and Maitland said she too is optimistic.

"I believe she's alive," she said. "I don't know why, I just do."

Members of a Facebook page have posted messages on behalf of Victoria's uncle, Rob Stafford, in which he asks that the person or people who have Victoria contact him to arrange a meeting and leave her with him, with no questions asked.

He said so far there have been no replies. But 28,000 people have joined a Facebook group coming out in support of the family.

About 1,000 community residents attended a candlelight vigil Sunday for the girl and Victoria's aunt, Rebecca Stafford, says it heightened the family's emotions.

"With all of the community coming out to show their support, at least we feel like our hope has been strengthened," she said.

Stafford also applauded the work of authorities involved in their search, adding, "I encourage them to keep up the hard work."

At Sunday's vigil, the crowd, some wiping away tears, raised candles to the night sky and said silent prayers that Tori would be found soon and brought home safely.

Tori's mother and father, who are separated and also have a 10-year-old son, thanked the community for their support during an incredibly difficult time.

"I know in my heart that she's OK and that we're going to find her," Tori's mother Tara McDonald said. "It's just a matter of time."

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