As harsh as this may sound, Blue might be headed to a "kill sale". Not meaning he will be sold for slaughter, but kill sales are some of the easiest places to get rid of a horse with no questions ask. I know you are not from Ontario but try contacting OLEX (Ontario Livestock Exchange) or the equivelent in your area. Many stolen/missing horses pass through sales there.
Kate is very right I hate to say. I've heard a lot of stories about this, including one about a quarter horse named Summer Breeze. Summer was taken by some people who the barn owner had hired to care for the horses and was taken to an auction, no questions asked. (Most auctions don't really check for proof of ownership.) Luckily, she wasn't sold to a killer buyer, but to a family. A few months later, the owner saw Summer in a field and asked the family were they got her. She had a brand, so she was given back to the real owner.