Firefighters and harbor control were combing the beach area looking for the man. The area remained closed to tourists due to risk of landslides, ANSA reported.
Earth and rocks tumbled when the 4.4-magnitude earthquake hit Ancona Thursday.
No serious damage had been reported from the quake, firefighters said, and no injuries were reported.
The missing man may have distanced himself from the scene on his own, officials told ANSA.
The quake had the same epicenter as a 4.9-magnitude quake that rattled the area a month ago.