The Walt Disney World Lost and Found department is amazing! My designer sunglasses flew off during Big Thunder Mountain Railroad and I thought they were gone for good. I called the Lost and Found department and described what day and location I lost them, gave a description of the glasses, and to my surprise, in true Disney Magic they were found! (Allow 24-48 hours for cast members to process your lost items.) - Michelle
You can report missing items at Guest Relations in the theme parks, but if you don't discover the item has been lost until you get home, try calling Theme Parks Lost & Found: (407) 824-4245. They're open seven days a week between 9 a.m. and 7 p.m. EST. Give them a description of the item and where you lost it, and if it's been turned in, they'll let you know.