Searching in the Liferay System Settings does not work without reindex. Please note that I experienced this issue since Liferay 7.0 and had it on all Liferay versions. I also tested this on Master from December (Commit 6110765cc846f66975e7a7124940211ffb05be41) with the same result.
Steps to reproduce:
1) Start a clean Liferay (with embedded search)
2) Go to Control Panel -> Configuration -> System Settings
3) Type "Analytics" into the Search box
Expected Result: "Analytics" is found (it is the first Icon in the Platform list)
Actual result: Search comes up empty
Now go to Search and reindex everything and retry. Reindex fixes the issue.