First thing to do: get to the nearest U.S. embassy or consulate. According to the U.S. Department of State, they can help U.S. citizens who’ve lost a passport abroad. That’s literally part of their job. You can also call them if you can’t physically get there — from the U.S. or Canada dial 888-407-4747, or from anywhere else in the world call 202-501-4444.
When you show up, you’ll need to bring a few things. The U.S. Department of State says to bring proof of U.S. citizenship — something like a birth certificate or a photocopy of your missing passport can work. You’ll also want to bring some form of ID, like a driver’s license or an expired passport if you have one. If your passport was stolen (not just lost), it’s also smart to have a police report with you.
If your passport was stolen, report it to local police first to get that report — it documents what happened and protects you if someone tries to use your stolen passport. USAGov also notes that if you’re back in the U.S. and find your old passport later, you should turn it in to the U.S. Department of State’s Consular Lost and Stolen Passport Unit.
One thing to know: emergency passports issued abroad often have limited validity — sometimes just one year — so you may need to renew once you’re back home. That said, they’re fully valid for travel back to the United States.
The single most important thing to remember: a photocopy or photo of your passport stored separately from the actual passport — like in your phone or email — could be a lifesaver. If the real one goes missing, that copy can serve as supporting proof of citizenship when you walk into the embassy.