The 15-year-old was riding his bike along the seafront esplanade in Foz at about 6:30 p.m. Sunday when a giant wave struck and he was swept out to sea, ThinkSpain reported.
Authorities combed the area overnight for the teen's body.
Twenty-seven cars were filled with water when waves hit the town of Ondarroa, ThinkSpain said.
The largest waves have been measured at more than 36 feet, ThinkSpain said.
A number of buildings have also been damaged due to the waves.