The accident happened last Wednesday in Sanford, Fla. Dana and Mark Gerstle and their two children were trapped inside a blue Ford Explorer SUV that had rolled over after traveling off the highway at about 5:45 p.m., the Seminole County Sheriff's Office said in a statement.
Zimmerman and another man helped the family out of the vehicle before deputies arrived. It was apparently the first time he has been seen in public since his acquittal.
"The vehicle is still there. It's on its side. There's people in there. They're getting them out of the car right now," a 911 caller told a dispatcher.
The sheriff's office says Zimmerman spoke with a deputy at the scene and then left.
ABC News contributed to this report.