Custom Panel Pane: This is for user pages, replace 'user' with node and replace artist_profile with your module.

Custom Panel Pane

<?php

/**
 * Implementation of specially named hook_ctools_content_types()
 */
function artist_profile_share_ctools_content_types() {
    return array(
      'single' => TRUE,
      'title' => t('Custom Share Links'),
      'icon' => 'icon_node.png',
      'description' => t('Displays Facebook Share button'),
      'required context' => new ctools_context_required(t('Profile Owner'), 'user'),
      'category' => t('Custom'),
    );
}

function artist_profile_share_content_type_render($subtype, $conf, $panel_args, $context) {
  $node = isset($context->data) ? drupal_clone($context->data) : NULL;
  $items = array();
  $output = '';
  $block = new stdClass();
  // dsm($context);
  
  $domain = (isset($_SERVER['HTTP_HOST'])) ? 'http://' . preg_replace('`^www.`', '', $_SERVER['HTTP_HOST']) : 'http://artspan.org';
  
  $path = drupal_get_path_alias('user/' . $context->argument);
  
  $title = ($context->data->field_artist_name) ? $context->data->field_artist_name : $context->data->title; // Add other text here if you want (such as "[artist name] on ArtSpan")
  $safe_title = str_replace(' ', '+', $title);
  
  $output = '<a href="http://www.facebook.com/sharer.php?u=' . $domain . base_path() . $path . '&t=' . $safe_title . '"><img height="16" width="16" title="" alt="Facebook" src="' . $domain . base_path() . drupal_get_path('module', 'artist_profile') . '/images/facebook.png"> Share</a>';

  $block->module = 'artist_profile';
  $block->delta  = 'unknown';
  $block->content = $output;
  // $block->content = theme('item_list', $items);
  return $block;
}

function artist_profile_share_content_type_admin_title($subtype, $conf, $context) {
  return t('Share');
}

function artist_profile_share_content_type_edit_form(&$form, &$form_state) {
  // provide a blank form so we have a place to have context setting.
}