Searching Quizlet is currently not working. There seems to be a problem on Quizlet's side. I've contacted Quizlet and am waiting for a response. I expect this to be fixed within a couple days.
As a workaround, you can login to Quizlet within Flashcards Deluxe to download personal sets. First go to Quizlet.com, find the set you want to download to the app, and either:
1) "Copy" the set, which will allow you to copy this as a new personal set
2) Create a folder called "Favorites", and click "Add to Folder" to add a set to this new folder.
You'll then see these sets in Flashcards Deluxe after tapping +, Quizlet, my Quizlet.com sets.
Ernie