<?php $search_text = empty($_GET['s']) ? "Search" : get_search_query(); ?> 
    <form method="get" class="input-append control-group btn-box" action="<?php echo esc_url( home_url( '/' ) ); ?>/"> 
        <input type="text" name="s" id="s" placeholder="Search" />
        <button class="btn"><i class="icon-search"></i></button>
    </form>
