The dresses were among items to be auctioned off in New York at a fundraising event for the Amy Winehouse Foundation early next year.
"People need to know they are not supposed to be out there on the market and they should not try to buy them," a family spokesman told the BBC. "The dress Amy wore on the cover of 'Back to Black' sold for $65,000 last year and the money went to the foundation, and another dress sold for $48,000 so the wedding dress could have raised as much as $161,000."
The Metropolitan Police said a formal report regarding the missing garments has not yet been filed.
The Grammy Award-winning singer died of alcohol poisoning in July 2011. She was 27.