I actually do possess a search form.

       <form method="get" id="searchform" action="<?php bloginfo('siteurl');?>">
         <div class="search_bx1"><input type="text" class="field" name="s" id="s" placeholder="<?php esc_attr_e( 'Search', 'mclaren' ); ?>" /></div>
         <div class="search_btn1">
         <input type="image" class="submit" name="submit" id="searchsubmit" src="<?php bloginfo('template_directory'); ?>/images/search_btn.jpg" width="22" height="20" value="<?php esc_attr_e( 'Search', 'twentyeleven' ); ?>" />
        </div>
     </form>

I have to hide the look co-ordinates in the url.And so i think i have to alter the form approach to publish.However when i alter the form action the redirection does not happen to search.php rather it is going to index.php.How do i overcome this.Help?

I stick to the default search method then the theme 'twentyeleven'

You need to alter the method attribute, not the action

<form method="POST" id="searchform" action="<?php bloginfo('siteurl');?>">

A control button and css would solve the problem..

      .search_btn1{
         background:url(images/search_btn.jpg) no-repeat;
          width:20px;
         height:20px;
          border: 0;
         cursor:pointer;
       }