The easiest things to do are sometimes the hardest to find.
If you are frustrated with searching for your items in Dynamics via the Entity Search box even after enabling your field for search, you need to do one more step. Go to your entity, navigate to the quick find view and then selecting the field you want to search on.
From there, you will then be able to search against your entity by the field(s) selected.
Easy to miss but easy to fix.