First of all, it works on my test install. I guess it depends on what you are searching for. I’m searching for ‘hello’ and the post ‘Hello World’ shows up fine.
Second, I get the following notice for this bit the_post_thumbnail( 'thumbnail', $attr );:
PHP Notice: Undefined variable: attr
Third, just to be a perfectionist, I would put elseif instead of if right here:
<?php } if( get_post_type() == 'articulo' ) {?>