Stephen Gutierrez rushed onto the dock and banged on the door of the boat after he saw the smoke.
The 27-foot boat tied up to the dock at 550 Marina Pkwy caught fire just before 7:30 a.m.
Video from a mobile phone captured the white smoke that quickly filled the air.
When Gutierrez realized no one was inside, he and some other bystanders helped untie the burning boat from the dock.
They worked together to push it away so as to protect the other boats moored there.
Gutierrez said boat owners have to be looking out for each other.
"We're a family here, like boaters," he said. "You can't just stand by and let one another go through difficult times."
The teenager also recorded the boat's registration number.
Chula Vista Police officers say they've identified and are working to contact the boat owner.