Having experienced the loss of a puzzle piece I know how frustrating it can be to have put in the time and then, one piece to go, its not there. In my case, someone hide it so they could put in the final piece. I wish they had been home when I needed it, would have saved me time and frustration in searching. Sometime, its not a puzzle hider, the piece for some reason is just not there. When you have tried all to find it, there is some information from puzzle makers on what to do.
RAVENSBURGER: It's frustrating when missing pieces ruin the fun. We would like to help! Please fill out this form with your information, the name of the Ravensburger product, the item number, and a brief description of your issue. Please understand that we cannot send complete gameboards, complete color sets, or complete game contents. Unfortunately, we also cannot replace accessories that are no longer in stock. You can access their form at https://www.ravensburger.us/service/replacement-parts/index.html
EDUCA: To request a lost piece, you should fill out the form you'll find on our website, Consumer Care Lost Pieces - Request. If you're unsure about the data you need to file your request, follow the instructions on the puzzle box which details how to find the piece's coordinates (A/B) and the puzzle's registration number.
It is important that you follow these instructions precisely and that you provide all the data requested. Otherwise, we may not be able to process your request or you may receive the incorrect piece.
This replacement service is limited to a maximum of 16 pieces per puzzle. Delivery of your piece normally takes between 4 to 6 weeks. At this time, this service is provided free of charge. https://www.educaborras.com