Search Filter (to return results by post type). Create a custom search form where you can set a hidden input to search that specific post type...see below the PHP block.

searchfilter.php

<?php
function otg_optional_search_filter($query) {
	$post_type = $_GET['type'];
	if (!$post_type) {
		$post_type = 'any';
	}
    if ($query->is_search) {
        $query->set('post_type', $post_type);
    };
    return $query;
};

add_filter('pre_get_posts','otg_optional_search_filter');

// Search form below allows you to pass a hidden input called "type" whose value will be parsed through the search function
?>
<form class="form-search" method="get" action="<?php bloginfo('url'); ?>" id="searchform">
  <input type="text" placeholder="search the site" class="input-medium search-query" name="s">
  <input type="hidden" name="type" value="post" id="type">
  <button type="submit" class="btn">Search</button>
</form>
<?php 
// You can additionally use more than one post type by setting the inputs up as arrays, seen below:
?>
<form class="form-search" method="get" action="<?php bloginfo('url'); ?>" id="searchform">
  <input type="text" placeholder="search the site" class="input-medium search-query" name="s">
  <input type="hidden" name="type[]" value="page" id="type">
   <input type="hidden" name="type[]" value="post" id="type">  
  <button type="submit" class="btn">Search</button>
</form>