Search is really a player-facing combat action specific for conducting an Active Perception check, but the Hide rules only say to do a Perception check, and the DM can use Passive Perception instead to speed up combat. However, outside of combat the DM can just call for a PC to do a Perception check per the DMG. A DM can just roll Perception when a PC tries to sneak by an enemy against the PC's Hide roll resultFind = use an action to search according to the rules shown in the early hiding threads. No action to find, no findy.