SharePoint 2013 Remove Search box in Master Page
Open master page in SharePoint Designer.
Search for DeltaPlaceHolderSearchArea.
Then remove below code.
<SharePoint:AjaxDelta id="DeltaPlaceHolderSearchArea" BlockElement="true" CssClass="ms-mpSearchBox ms-floatRight" runat="server">
<asp:ContentPlaceHolder ID="PlaceHolderSearchArea" runat="server">
<div id="searchInputBox">
<SharePoint:DelegateControl runat="server" ControlId="SmallSearchInputBox" />
</div>
</asp:ContentPlaceHolder>
</SharePoint:AjaxDelta>
<asp:ContentPlaceHolder ID="PlaceHolderSearchArea" runat="server">
<div id="searchInputBox">
<SharePoint:DelegateControl runat="server" ControlId="SmallSearchInputBox" />
</div>
</asp:ContentPlaceHolder>
</SharePoint:AjaxDelta>
