When searching for a friend bear in mind that nicknames are case-sensitive.  What this means is that the names "twelveletter" "Twelveletter"  Twelveletter" and "TWELVELETTER" are all separate and different accounts.  So double-check to make sure you are putting capitals in the correct place.

Eternity Warriors 4 cannot be played cross platform, so if you are on an Apple device and your friend is on an Android device, or vice-versa, you will not see each other.  Both players must be using the same platform: Apple user with Apple users, Android with Android.

This also applies to players who have downloaded from Amazon or Google Play - the Amazon and Google Play games are separate so you'll only see the other players who have downloaded from the same store, even if you are both playing the same Android device.