[Plugin: Video Thumbnails] fetching video thumbnails upon frontend post creation

I’m using the plugin Video Thumbnails to fetch thumbnails from a video url specified in a custom field.
It works great in the bakend, but on my site the posts are submitted on the front end with this code:

<?php

if( 'POST' == $_SERVER['REQUEST_METHOD'] && !empty( $_POST['action'] )) {

	if (isset ($_POST['title'])) {
		$title =  $_POST['title'];
	} else {
		echo 'Please enter a title';
	}
	if (isset ($_POST['description'])) {
		$description = $_POST['description'];
	} else {
		echo 'Please enter the content';
	}

	$video_url = $_POST['videourl'];

	$post = array(
		'post_title'	=> $title,
		'post_content'	=> $description,
		'post_status'	=> 'publish',
		'post_type'     => 'post',
	);
	$the_post_id = wp_insert_post($post);

	update_post_meta( $the_post_id, '_videoembed', $video_url);

	wp_redirect( home_url(dashboard) ); 

}
do_action('wp_insert_post', 'wp_insert_post'); 

?>

How do I launch the functionality of the plugin after submitting the new post?
So that the video thumbnail is fetched from its source and set as post_thumbnail…