Montreal police say they believe a 10-year-old boy who disappeared last week accidentally fell and drowned in the Rivière des Prairies.

Ariel Jeffrey Kouakou was last seen March 12 in des Bateliers Park, which borders the river, after he left his home in Ahuntsic-Cartierville to meet a friend.

"For right now, I can tell you that we're not capable of saying without a doubt that it's an accident, but that is the number 1 hypothesis," said Insp. Ian Lafrenière.

"That's why the investigation is ongoing."

Lafrenière said Ariel was last seen by a woman who also spoke to him in the park around 11:25 a.m. that morning.

"She left the park. We have cameras that show that young Ariel entered the park, but we do not have any that showed he left it," he said.

In the days since Ariel was last seen in des Bateliers Park, police officers and volunteers have combed the neighbourhood and surrounding areas by foot, horseback, helicopter and boat.

The parents of Ariel Jeffrey Kouakou have said they believe their son is alive and was abducted. (CBC) Divers also spent Monday and Tuesday submerged in the water of the Rivière des Prairies, but after no signs of Ariel were found, that search was called off by police.

The boy's father, Kouadio Frédéric Kouakou, has repeatedly said he believes his son is alive and was abducted. Their family won't give up on trying to find Ariel, he said.

"My family and I, until proven otherwise, maintain the theory [that it was] an abduction. I'm firm on that. I'm really, really firm on that," he told reporters on Thursday.

He said that while he respects the police and their investigation, he wants all possible leads to be explored.

Kouakou also called on Montrealers and Quebecers to remain vigilant in the search for his son.

"We haven't yet fulfilled our goal, which is to find Ariel. I want us to keep the flame alive to continue our search."

Kouadio Frédéric Kouakou, Ariel's father, says he maintains his son was abducted (Radio-Canada)

The situation has been hard on his family, especially his wife and young daughter, Kouakou added.

"Yesterday, [my daughter] asked me, 'Where is Ariel? Is Ariel there?' Those are the questions coming from a little girl. How can I reassure her? How? I don't have the words for that."

Lafrenière said the investigation is ongoing and police "haven't closed the door" on any scenarios, but they do believe what unfolded that day was a tragic accident.

"As a father, as a police officer, I hope for the best. Believe me," he said. "And we want to answer that question where is he and what happened?"

'Unprecedented' help

As their investigation continues, police have received nearly 700 tips from the public so far. Lafrenière said more than 500 volunteers also showed up to help canvass the neighbourhood.

"It's unprecedented," said Lafrenière. "Over the past 25 years, I have rarely seen the public react this way."

There is also a $100,000 reward in place to elicit new information that leads to Ariel.

Montrealers started to pledge money after the family initially offered $10,000 to anyone with information about their son's whereabouts.

Here are details about Ariel, who speaks French:

About four-foot-seven, weighs 88 pounds.

Dark hair and dark eyes.

Was last seen wearing a black coat with a hood, grey pants and yellow shoes.

Anyone with information about Ariel's disappearance is asked to contact 911.

They are also invited to visit the command post set up outside Galéries Normandie on de Salaberry Street, which is about 500 metres from the park.

Police are also asking residents who live near the river in Ahuntsic-Cartierville to be vigilant and contact police if they see any signs of Ariel.

Lafrenière said police officers and emergency responders will continue to search near the riverbank.