Hi,
You can use input type hidden in your search form to get a specific post type search result :
<div>
<h3>Search Products</h3>
<form role="search" action="<?php echo site_url('/'); ?>" method="get" id="searchform">
<input type="text" name="s" placeholder="Search Products"/>
<input type="hidden" name="post_type" value="products" /> <!-- // hidden 'products' value -->
<input type="submit" alt="Search" value="Search" />
</form>
</div>
You can change the post_type value in hidden input with your own post_type.