Custom Loop Query For Search Page

You have to pass the search query too. To get the search query, you can use the get_search_query() function, and pass it to the query’s s parameter:

$search_string = get_search_query();

$args = array( 
    's'              => $search_string,
    'posts_per_page' => 12,
    'order'          => 'DESC',
);