It's pretty simple to find your lost AirPods, so long as they still have power. Apple has a tool called "Find My iPhone" that, despite its name, can help you keep track of almost all your Apple gadgets.
The app is preinstalled right on your iPhone or iPad. If you don't have an iPhone, you can also find it at iCloud.com, where you'll just need to log into your Apple account first.
Here's what you need to do:
There's not much you can do if they stolen or are no longer within range of your iPhone, like in the back seat of an Uber somewhere. You might not have to buy a whole new set, though. If you've only lost a single AirPod, you can buy a replacement from Apple for $69 per bud. Or, if you just lost your case, you can purchase a new one for $59. Apple's new wireless charging case for AirPods costs $79 to replace.