The trailer, containing thousands of graphic novels and comics, was taken from a car park outside Corner Store Comics in Anaheim, California, on March 20.
The publisher was taking its stock, which included display equipment, signage and limited edition comics, from WonderCon to the Emerald City Comicon in Seattle, Washington.
"We are working with local law enforcement, but we could really use your eyes and ears on the ground," Avatar editor-in-chief William Christensen said in an announcement on Bleeding Cool.
"Retailers on the West Coast in specific, if anyone approaches you with large quantities of Avatar books for sale, please let us know. Diamond is our exclusive distributor, there would be no one else who would have deep inventory on our books who should be trying to sell off the street to you.
"Readers and fans, if you see someone at a small local convention trying to dump loads of Avatar books or anything else that seems suspect, do please drop us a line."
Christensen assured fans that the publisher has back-up stock which will ensure that retailers are not affected by the loss.
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