Sorting, reordering/moving, search, … playlists are unfortunately the worst part of Plex. 
Let’s say you have a list of 500 videos or songs and you want to move the 5 last songs to the top. You have to drag the song, scroll ALL the way up (takes forever), then drop it - FIVE times! You can’t select all five and move them. You can’t just overwrite the index number or something (497 → 1, enter). There isn’t even a “move to top” shortcut.
And yes, you also can’t see / search for a specific track in the playlist - because there’s no search feature.
Please drastically improve playlist management.
Edit: Just noticed that my comment is also related (but not only limited) to this: Mass Reordering of Playlists
