The 21-year-old Dallas native was swimming on a sandbar around 7:30pm when something went wrong.
Friends say he stepped into a hole and was swept away by the current.
The Coast Guard is using a helicopter and a boat in the search.
The San Luis Pass is notorious for its dangerous currents.
"Every year the Coast Guard responds to multiple cases involving distressed persons in the water in the San Luis Pass area," said USCG Capt Brian Penoyer. "Signage on all the beach access entrances indicate the known extreme conditions with currents and drop-offs and visual NO SWIMMING logos. Yet people still take a chance."
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