A responsive design is a key to mobile first design approach. With increasing number of users transacting and browsing on small/smart devices, it is imperative for a website/web store to be optimized for increased goal conversion on smart phones and tablets.
Search is a very important function of any web and mobile app project. Depending on the nature of the project emphasis on search needs to be implemented. For example for CMS sites search all content not just pages, post but also all custom objects. If it is an eCommerce implementation, then in addition to searching product catalog, static content and blog; we implement predictive/type ahead search, weight based/weighted search, etc.