Problem Description: Unable to search a file or folder even if it really exists on the site.
Resolution 1: Make sure that the site is allowed to appear in search results.

  1. Click Site Actions, and then click Site Settings.


  2. Under Search section, click Search and offline availability.

  3. In the Indexing Site Content section, under Allow this site to appear in Search results, select Yes to allow the content of the site to appear in search results or No to prevent the content from appearing in search results.


  4. If the above steps does not resolve the issue, proceed to Resolution 2.


    Resolution 2: Re-index the site.

    1. Follow the above steps 1-2.
    2. Click on Reindex site button and wait for the process to finish.




    Reference link: https://support.office.com/en-us/article/Enable-content-to-be-searchable-d7ba92db-8618-43fe-87ee-adf03d973062?ui=en-US&rs=en-US&ad=US#bm3