How to prevent Content type from appearearing in built-in Search results
There are two modules you can check out.

Search Config


  Restrict search results by the content type. This is a role based
  restriction.


Search Restrict


  Restrict by role who can search for each content type.
  
  Approach of this module is to re-write the search query, so that
  content is indexed and available as search results to users in role(s)
  that have permissions to view it, but not displayed to other roles.


OR 

You can write your own query alter function.

function mymodule_query_alter(&amp;$query) {
  $is_search = FALSE;
  foreach ($query-&gt;getTables() as $table) {
    if ($table['table'] == 'search_index') {
      $is_search = TRUE;
    }
  }

  if ($is_search) {
    $query-&gt;condition('n.type', 'node-type-name', '&lt;&gt;');
  }
}


And yes as webkenny suggested Custom Search as well.


  Basic options
  
  The module adds options to select:
  
  
  which content type(s) to search,
  which specific module search to use (node, help, user or any module that implements search),
  advanced criteria
  
  
  For all these choices, there are options to switch between a select
  box, checkboxes or radio buttons, and also customize the selector
  label and the default - Any - text.