I lost my Magic Band+ at Disneyland. I was wearing a big, bulky sweater, and while I was walking and taking it off, it must have pulled my Magic Band+ off my arm without my noticing, and dropped on the ground somewhere. Once I realized it was missing from my wrist about 30 minutes later, I was devastated, and pretty certain I wouldn't get it back.
I walked over to Guest Services and asked half-heartedly about a Lost and Found. They told me that there was one outside the entrance of Disneyland, but instead of visiting it, there was a feature on the Disneyland app I should use to report my lost item.
Surprised I'd never noticed this feature, I opened my app and spotted the link. It asked me specific questions about my item, including where I thought I might have lost it, what time I thought I lost it, etc and then asked for my contact information.
A few hours later, I received an email that my lost item had been retreived and I could pick it up at the Lost and Found OR have it mailed to me.
By park closing, I had my Magic Band+ back. I was thrilled.
Here's a step by step video of how to use the Lost and Found feature.