A young man who was struck and killed by a GO train in Mississauga yesterday is being remembered as an 18-year-old "athlete with a good heart."

Jafari Williamson was killed soon after he stepped off the westbound train at Clarkson station with a couple of friends at around 12:30 p.m. Saturday.

Paramedics rushed to the scene to help Williamson. He was conscious and breathing when paramedics arrived but authorities determined he had very serious injuries to his legs and called for an air ambulance.

He was transported to the trauma center at St. Michael's Hospital in Toronto, but died sometime before 4 p.m.

Police say it was likely a death by misadventure.

"It was a tragic accident and I would hope that everyone would obey the safety rules and understand there is zero forgiveness with trains that weigh in excess of hundreds of tons," said Peel police Const. Wayne Patterson.

Friends and family of the teen created an online tribute to him on Facebook, a popular social networking website.

Williamson, who was once a student at Port Credit Secondary School, had a "big, beautiful smile and a big heart," said one girl.

"You never had one mean bone in your body," she wrote on the site.

Several people remarked on his kind heart and willingness to be there for his friends.

"Jafari always had a smile on, he didn't care who was there or who they were, we would always crack a joke and get a smile out of everyone," said one young man who went to high school with the teen.

One person remembered Williamson as the friendly face at a new school.

"You were the first person to talk to me when I was new in school and was always laughing and smiling and jumping over stuff," he wrote on Facebook. "I'll miss you man."

Police are still tying to figure out how the teen ended up in the path of the train as it readied to leave the station.

A security camera is installed on the property but it wasn't recording at the time of the accident because of construction work on the site.

Police are looking to speak with witnesses who were at Clarkson station at the time of the incident. Witnesses are asked to call investigators at 905-453-2121, ext. 3710.

With a report from CTV Toronto's Zuraidah Alman