WordPress Posts Id from query_posts

Hi community,
I’m using wordpress with a template that generates a pretty nice thumbnail for each post depending on ids, and type of post. (ref:https://blinkdemo.wordpress.com/)
I have been asked to create a query for a template page that checks the page slug and then list the posts containing a certain category + a tag (‘comparativas’).

$args = 'cat='.$idCategory.'&tag=comparativas';
 query_posts( $args );

The problem that I’m facing is that the list of post presented on the page doesn’t show up the corresponding thumbnail on each post.
Even when :$current_id = get_the_ID(); shows the correct Id if It’s echoed on the loop, I couldn’t make the template work properly.

Thumbnails are generated dynamically basically with these lines:

$post_id = $post->ID;
    $thumbnail_id    = get_post_thumbnail_id( $post_id );
    $thumbnail_image = wp_get_attachment_image_src( $thumbnail_id,$thumbnail_size );

The problem is that I could’n find the way to send to the specific post ids to the function above, since the main$wp_query->posts; retrieves the page id instead of the post requested by the query_posts method.

Do you know how to retrieve the nested id’s or rewrite the values on the main $wp_query?
If you have any clue that could help me to resolve this I will really appreciate it.

Thanks in advance