You have a search box over your list or library and I don't! Why?
SharePoint 2013 has added a search box to most lists and libraries that is scoped to the current list. When the user performs the search they will stay in the list’s page. They will not be redirected to a search results page. They can continue to sort or filter the results using the column heading dropdowns.
Pretty cool! But it's missing in my library!
Four Reasons You Might Not See It
#1 - Turns out that this search box is only available in one View Style. If you have not played with View Styles then take a look at this article http://techtrainingnotes.blogspot.com/2010/05/sharepoint-list-view-styles.html That's an older article, but still applies to SharePoint 2013.
If you pick any style other than Default, you lose the search box. Bummer…
#2 - It's only available in the Enterprise Edition of SharePoint 2013. I'm guessing that it may only be available in Office 365 / SharePoint Online in the "E" subscriptions.
#3 - It can be disabled! Edit the page, edit the web part, expand the Miscellaneous section: It is enabled by default in list/library pages. It is disabled by default when you add a list/library web part to a page.