Can't get featured image to appear.

Been at this for hours and now I’m PLEADING for help.

<?php
 $events = eo_get_events(array(
         'numberposts'=>3,
         'event_start_after'=>'today',
         'showpastevents'=>false,//Will be deprecated, but set it to true to play it safe.
		  'tax_query'=>array( array(
                         'taxonomy'=>'event-category',
                         'operator' => 'NOT IN',
                         'field'=>'slug',
                         'terms'=>array()))
    ));

  if($events):
     echo '
<ul>';
     foreach ($events as $event):

          //Check if all day, set format accordingly

		  $format = ( eo_is_all_day($event->ID) ? get_option('date_format') : get_option('date_format').' '.get_option('time_format') );
          printf(
             '
<li><a href="%s"> %s </a> on %s </li>
',

             get_permalink($event->ID),
             get_the_title($event->ID),
			 get_the_post_thumbnail( $thumbnail->ID, 'thumbnail' ),
             eo_get_the_start($format, $event->ID,null,$event->occurrence_id)
          );
     endforeach;
     echo '</ul>
';

  endif;
 ?>

What am I doing wrong? UGHH.