The unidentified family had been sailing a small vessel west of Monterey Bay, where strong winds, cold water and big swells made for perilous conditions. Forecasters had issued a weekend advisory warning boaters of rough seas in the area.
The group - which included two children under 8 - was approximately 65 miles off Monterey when their first distress call came in around 4:20 p.m. Sunday, Coast Guard Lt. Heather Lampert said.
The boaters said their 29-foot sailboat, which might have been called "Charmblow," was taking on water and their electronics were failing, Lampert said.
An hour later, the family members reported they had to abandon the boat and were trying to make a life raft out of a cooler and life-preserver ring, she said. The Coast Guard then lost radio contact.
The agency has not identified the family, although investigators were able to determine from the broken distress calls that they were a husband and wife, their 4-year-old son and his cousin, Lampert said. The Coast Guard has received no missing persons' reports.
The family's location initially was reported farther north, but Lampert said investigators using the boat's radio signal and radar now believe the call came in west of Monterey Bay, which is about 100 miles south of San Francisco. The boat did not have a working GPS system.
The National Weather Service had issued an advisory throughout the weekend warning boaters of strong winds and rough seas around the San Francisco Bay Area. Water temperatures in the area typically are in the 40s and 50s, making long-term survival difficult.
Mariners "operating smaller vessels should avoid navigating in these conditions," the advisory said.
Calls to harbors in California have failed to locate the boat, and database searches have come up empty too, Lampert said. The Coast Guard was expanding to Hawaii, the Seattle area and north into Canada.
Lampert said Coast Guard crews searched for the family through the night. A California Air National Guard helicopter was assisting with the effort.