A man in his early 20s who swam across the mouth of Drakes Estero with two others during a family outing on Labor Day vanished during the return swim, which coincided with an incoming tide, said Point Reyes National Seashore spokesman John Dell’Osso. The park, a water team, a dive team and two helicopters have all aided in the search for the missing swimmer, whose identity has not been released. (The fog, however, prevented the…