More than 400 people braved freezing winds and lashing rain on Monday night to offer support for Riley Mercer, a Newfoundland teenager battling a rare type of brain cancer.

Participants stood on the Mercer family's lawn in Conception Bay South, just west of St. John's, and sang songs, read prayers and held lights aloft.

Many spoke of their deep sympathy for the Mercer family, whose daughter Alex died of the same disease when Riley was just a small boy.

Louise Mercer

Louise Mercer told friends of how her son Riley supported her through the death of her daughter, Alex. (CBC)

"When Riley was just three years old, his big sister Alex was diagnosed with a cancerous brain tumour," Riley's mother, Louise Mercer, told the crowd.

"The next 15 months were what I thought were the longest most horrible 15 months of my life. Little did I know then that my life was going to get much worse."

Riley was inside the house, just metres away from where hundreds sang songs such as Amazing Grace. He was unable, however, to see or hear the proceedings, as his disease has taken away his sight and hearing. 

Louise Mercer told the gathering that after Alex died almost 11 years ago at the age of nine, Riley would always reassure her that things would be all right.

"I would always tell Riley, you'd better not go before me," she said, struggling to speak.

"He would always laugh and say, 'I won't.' Well, Riley Mercer, I'm going to tell you one last time, you'd better not go before me."

Riley Mercer's story has deeply touched neighbours, friends and even those who have never met the family. In a matter of days, students, teachers and parents at Villa Nova Junior High raised more than $14,000 to support Riley's parents while they stay home to care for him.

Hoping for a miracle

Family friend Rick Webber said Riley is a remarkable boy.

"He never complains. He hasn't complained once throughout this entire ordeal," he said.

"I just wish that everybody's prayers and hopes for a miracle would come true for this family. It's really tough, but tonight is a great night for them."

Denise Sparkes, a friend of the family, said people are holding out hope.

"May God heal him, and take care of him," she said.

"He's such a special child and they are such a special family."