Please note that the AirPlay menu has been moved in iOS 11.

Find the AirPlay menu like this: 

1. Swipe up on your iPhone/iPad to get to the Control Center
2. The Music section is located up on the right hand side
3. Click the 'waves' to go directly to the speker list
4. If you have more than 4 AirPlay devices remember to scroll down to find the rest of your speakers