A Cape Breton family says social media helped police arrest a suspect in a hit-and-run accident last week in Sydney.

Robin McGean and her pregnant cousin were driving through the intersection at Prince and George streets when she says a car ran a red light and smashed into their vehicle. The driver didn't stay at the scene.

"All of a sudden I felt the car in the side of me," McGean said. "We were spun around and everything was smashed."

McGean said the door on the passenger side was crushed and trapped both women inside. She said her first thought was for her cousin.

"I heard my cousin scream, 'The baby, the baby' and I immediately called 911," she said.

McGean was cut out of the car by rescue workers and both women were taken to hospital where doctors said they were OK.

After calling police, McGean turned to Facebook. She described what happened in a post to her page and asked for help to find the other driver.

Robin McGean, hit-and-run accident victim

Robin McGean and her pregnant cousin were driving through an intersection in Sydney when she says a car ran a red light and smashed into their vehicle. (CBC)

People posted details of the suspect on the social media site and it was enough information to help police find him.

McGean said it was the power of social media at its best.

"I have no doubt in my mind that it helped us 100 per cent find whoever did this," she said.

McGean said police told her the suspect has no licence and no insurance. A man has been questioned about the crash, but no charges have been laid.

Her mother, Colleen McGean, said it was terrifying but could have been a lot worse.

"I feel blessed the girl made it out alive. Money can't replace their lives or if one had to be quadriplegic or the other girl had lost the baby, that would be more devastating," she said.