How to add a search functionality to a Wordpress theme?

[admin]

I've been asked to add search functionality to a Wordpress theme that has neither search.php page, is this possible? Is it possible using plugins?

The theme is this:
<a href="http://themeforest.net/item/heal-re....seg_1=search_item&amp;WT.z_author=raybreaker" rel="nofollow">http://themeforest.net/item/heal-re....seg_1=search_item&amp;WT.z_author=raybreaker</a>

Thanks