Select Page
<form class="search-xxx" role="search" action="<?php echo site_url('/xxx-url/'); ?>" method="get" id="searchform">
  <label>Search</label>
  <input name="xxx-value" type="text" required />
  <input class="button" type="submit" value="Search" />
</form>

<?php
$search = $_GET['xxx-value'];

$args = array (
  'post_type'	=> 'xxx',
  'tag' 		=> $search,
);

$query = new WP_Query( $args ); 

if ( $query->have_posts() ) {
  while ( $query->have_posts() ) { $query->the_post();
  $post_id = $query->ID;
  }
}