I have tested the new Plexamp on my iPhone as well as my Mac, and while I can definitely play music back, search seems completely broken, as you can see in this screenshot:
As you can see, I have a Nine Inch Nails song open in the player (that I navigated to from one of the “Recently” options on the home screen), but if I search for Nine Inch Nails (or anything else) I get no results.
My server is running 1.19.1.2645 on Ubuntu. I do have a rather large music library (~35k tracks). Let me know what other information I can provide to help debug this issue.