Wikipedia has its own search engine, with its search box on every page. The search box will go to a given page name, but there are three ways to go to the search results page instead.
If you activate the magnifying-glass icon (or the Search button) from an empty search box, you'll go to an empty search results page.
If you start any query with the tilde character, it always generates search results, ~page name.
Choose "Search for pages containing" from the page names that drop-down as you type (if you have JavaScript enabled). To access the suggestions that drop down as you type, click the mouse on them, or use ↓, or Tab ↹, to access them.
At an empty Search display, there are filtering options for:
Content pages – Search in (Article)
Multimedia – Search for files
Everything – Search of all content (including talk pages)