She was scheduled to unveil her 2010 collection at a charity event in downtown Los Angeles on Sunday.
Clancey says the clothes are of no value to the person or people who stole them.
"No one can do anything with it. You can't sell it, you can't put it on eBay, you can't... you cannot put it anywhere on the Internet, because we will find it," Clancey said. "So for six months work to have disappeared, that's over six months revenue for me."
She puts the value of the stolen goods at more than $300,000.
Clancey is offering a reward for the recovery of her designs.
Police are investigating.