The incident was reported at about 2:30 p.m. near the levee at Sharp Park Beach, just south of the Pacifica pier.
Witnesses say the man and his friends spent the afternoon drinking on the beach and that after the man disappeared under the waves, his friends left the beach.
"We saw this We saw this guy get into the water and two to three waves knocked him down really bad," said witness Mihail Matikov. "We could see something was going to happen."
Pacifica police said one of the friends went into the water to try to find the missing man but came back alone.The Coast Guard had initially reported there were four men and they had all been swimming.
Police say there are no laws that require people to stay at the scene of an emergency or to call for help. The man's identity has not been released.
The Coast Guard, which dispatched a helicopter and boat, searched 45 square miles along the Pacifica shoreline for nearly six hours before suspending the search Thursday night.