Custom Buttons in TinyMCE

I’ve been digging through all the Codex and the TinyMCE docs but I can’t get a new button on the tMCE editor. I want to add a new button to apply some classes to the selected element; it’s for a small plugin I’m doing. I don’t get an error code, but the button isn’t added.
This is the code:
thickbox.php

$thickboxPath = get_bloginfo('url')."/wp-content/plugins/thickbox/";
function myplugin_addbuttons() {
   if ( ! current_user_can('edit_posts') && ! current_user_can('edit_pages') ) return;
   if ( get_user_option('rich_editing') == 'true') {
     add_filter("mce_external_plugins", "add_myplugin_tinymce_plugin");
     add_filter('mce_buttons', 'register_myplugin_button');
   }
}
function register_myplugin_button($buttons) {
   array_push($buttons, "button");
   return $buttons;
}
function add_myplugin_tinymce_plugin($plugin_array) {
   $plugin_array['myplugin'] = $thickboxPath . 'tinymce/editor_plugin.js';
   return $plugin_array;
}
add_action('init', 'myplugin_addbuttons');

tinymce/editor_plugin.js

(function(){
	tinymce.PluginManager.requireLangPack('addthickbox');
	tinymce.create('tinymce.plugins.AddThickbox', {
		init : function(ed, url) {
			ed.addButton('button', {
				title : 'addthickbox.desc',
				image : url + './../images/class.png'
			});
		},
		createControl : function(n, cm) {
			return null;
		},
		getInfo : function() {
			return {
				longname : "AddThickbox",
				author : 'Elliot',
				authorurl : 'http://ilovecolors.com.ar/',
				infourl : 'http://ilovecolors.com.ar/',
				version : "1.0"
			};
		}
	});
	tinymce.PluginManager.add('addthickbox', tinymce.plugins.AddThickbox);
})();

tinymce/langs/en.js

tinyMCE.addI18n("en.addthickbox",{
	desc : 'Description'
});

Could you pleeeeaasssseee give me a hand? I just don’t know what I’m doing wrong, the image is in its place. Please, point me some tutorial, give me an advice, anything would help!!
Thanks in advance!!