Blues musician Fats Domino is among those missing after Hurricane Katrina. His agent, Al Embry, said he had not been able to contact him since Sunday.
The 77-year-old had told Mr Embry he was staying at his home in a low-lying area of New Orleans, with his wife, Rosemary, and their daughter.
Hundreds or even thousands of people are feared to have drowned in the city, where the hurricane struck on Monday.
Information is hard to obtain as power cables and telephone networks are down.
Domino's niece, Checquoline Davis, reportedly posted a message on an online bulletin board on Thursday pleading for information.
She reportedly wrote that Domino, his wife, their children and grandchildren "didn't get out" of the second floor of his house.
Mr Embry, who has worked with Domino for 28 years, said: "I hope somebody turns him up, but as of right now, we haven't got anybody that knows where he's at."
More than a million people were evacuated from New Orleans and the surrounding areas before the hurricane struck, but Mayor Ray Nagin has estimated that up to 100,000 people decided to stay in the city.
Hall Of Fame
The singer and pianist, whose real name is Antoine Domino, has sold more than 110 million records, including Blueberry Hill and Ain't that a shame.
He had nearly 20 US Top 20 singles between 1955 and 1960.
Among the last of them was Walking to New Orleans, a Bobby Charles composition that became a string-laden tribute to the city that inspired him.
In 1986 Domino was inducted into the Rock And Roll Hall Of Fame, and won Hall Of Fame and Lifetime Achievement awards at the 1987 Grammy's.
http://news.bbc.co.uk/1/hi/entertainment/4206622.stm