The call came into to the Coast Guard Sector New Orleans last night around 9pm.
A catamaran sailing southwest of Southwest Pass was in trouble and taking on water.
Two people from the stricken boat were rescued.
But another passenger, 38-year-old Cristina Castro, from Modesto, California, was missing.
Throughout Thursday the Coast Guard has been searching the open water for any sight of the woman.
Coast Guard assets, including a 45-foot Response Boat-Medium boat crew from Coast Station Venice and an MH-65 Dolphin Helicopter aircrew were dispatched from Airstation New Orleans to the vicinity. The 85-foot Coast Guard Cutter Sailfish, and an HC-144 Ocean Sentry airplane from Mobile, Alabama are all involved in the search for the woman.
The sector watchstanders issued an urgent marine information broadcast, which a Good Samaritan responded.
The Offshore Supply Vessel, Mr. Jake, was able to recover two people from the water, who were reported to be wearing life jackets and in stable condition.
Castro is described as a Latino female, last seen wearing a blue shirt, blue pants and black life jacket.