In default WordPress installations, the search function only yields results for posts. It does not search pages, comments, or anything else.
Search Everything from Dan Cameron solves that problem. Install and activate the plugin, and then go to Options > Search Everything to select what exactly you want to be searched. Here are the options:
- Only approved comments
- Custom fields (metadata)
I’m not sure why people would want users to see results in drafts or custom fields, but maybe there is a use for that that I’m not aware of.