"It's horrible that anyone would do this," Colleen said. "We just want whoever has it to give it back."
The tandem also provided some measure of independence for the young man who loved to ride dirt bikes when he still had his sight.
Darcy went blind in 2014, thanks to a tumour the size of an apple in his brain. He'd always had poor vision, but one morning he woke up to find his sight almost completely gone.
"I'd had the tumour since I was 4, and it had been misdiagnosed for 10 years. If it had been left for another four months, I would have died," Darcy said.
The tumour is still in Darcy's brain, but it's not growing. However, the loss of his sight is permanent.
"I really enjoyed riding the tandem, although sometimes I felt dizzy on it because I couldn't see," he said.
Colleen said there was no way she could afford to buy another tandem, as they were much more expensive than ordinary bikes.
She does not want to press charges against whoever stole the bike - she doesn't even want to know who it is.
"I just want the bike returned, no questions asked, for Darcy's sake," Colleen said.
The bike is a dark grey, 10-speed tandem, with a Pedal Pushers sticker on it, white foam rubber on the handle bars and blue foam rubber on the back seat.
The bike can be dropped off at 3 Smithfield Rd.
