Hi Lee,
Finder can't search against layers that are nested in the TOC of the web map. There's documentation on this here:
Configure Finder app - Get Started | ArcGIS for Local Government
Specifically, check out the info for step 2 under Find Settings.
You can search against the Parcels layer if you add it individually to the web map (REST URL should end in a layer index number).
-Allison
ArcGIS for Local Government