Search for posts with specific tag inside custom page template

I’m developing a WordPress blog where there are two custom pages – i.e., different from index.php. In there, there are two albums of photos, with the photos listed on a div above.

I’ve put an input so the user can type a tag and when he submits it, it will show on the album only the images of that specific tag.

The problem is that no matter what I put in the ‘action’ parameter of my input, it considers the action as ‘http://wordpressblogname.com/?name-of-my-input=value-of-my-input. That way, it searches on the index. I want it to search on the custom page that I created, so the search tag can filter the posts (images) from that page.

Can someone tell me how can I make it search on that custom page? Thanks.

Edit: Someone asked for the code. There it is:

<?php
$permalink = get_permalink( 55 );
?>
<form method=”get” action=”<?php echo $permalink; ?>”>
<input type=”text” name=”tag” value=”Procurar” onfocus=”if (this.value==’Procurar’) this.value = ”” onblur=”if (this.value==”) this.value=’Procurar’;”/>
</form>

<div class=”bottom-aluno”>

<?php
$args = array(
‘cat’ => 2,
‘tag’ => $_GET[‘tag-name’],
);

$wp_query = new WP_Query($args);
$size = array(162,171);
if (have_posts()) : while (have_posts()) : the_post(); ?>
<?php $src = wp_get_attachment_image_src( get_post_thumbnail_id($post->ID),”, false, ” ); ?>
” data-lightbox=”imagens-alunos”> <?php the_post_thumbnail(”, array(‘class’=>’universo-alunos-thumb’)); ?>

<?php endwhile; endif; ?>

</div>