While we're happy to announce the we've imlemented the ability to search tracks you've already synced on the Android platform, we haven't quite implemented the feature for iOS.
Please add your kudos to this idea if you'd like to see this implemented.
We're happy to say users can now sort and filter songs in their playlists on iOS devices. Just open your playlist and scroll to the top of the screen. There you will see the 'Filter' search bar and the option to sort just to the right. Thanks for your feedback everyone!