[jquery] TypeError: $(...).autocomplete is not a function

I am getting the above error using the following code inside a Drupal module.

jQuery(document).ready(function($) {
        $("#search_text").autocomplete({
            source:results,
            minLength:2,
            position: { offset:'-30 0' },  
            select: function(event, ui ) { 
                    goTo(ui.item.value);
                    return false;
            }        
    }); 
});

Jquery is definitely loaded, and I have tried using a different variable for $ - any ideas what else might be the problem?

(Edit) Drupal specific answer for autocomplete:

drupal_add_library('system', 'ui.autocomplete');

Just add these to libraries to your project:

<link href="https://code.jquery.com/ui/1.10.2/themes/smoothness/jquery-ui.min.css" rel="stylesheet"></link>
<script src="https://code.jquery.com/ui/1.10.2/jquery-ui.min.js"></script>

Save and reload. You're good to go.

Try this code, Let $ be defined

(function ($, Drupal) {

  'use strict';

  Drupal.behaviors.module_name = {
    attach: function (context, settings) {
        jQuery(document).ready(function($) {
      $("#search_text").autocomplete({
          source:results,
          minLength:2,
          position: { offset:'-30 0' },  
          select: function(event, ui ) { 
                  goTo(ui.item.value);
                  return false;
          }        
        }); 
        });
   }
  };
})(jQuery, Drupal);

Simple solution: The sequence is really matter while including the auto complete libraries:

<link href="http://code.jquery.com/ui/1.10.2/themes/smoothness/jquery-ui.css" rel="Stylesheet"></link>
<script src='https://cdn.rawgit.com/pguso/jquery-plugin-circliful/master/js/jquery.circliful.min.js'></script>
<script src="http://code.jquery.com/ui/1.10.2/jquery-ui.js" ></script>

In my exprience I added two Jquery libraries in my file.The versions were jquery 1.11.1 and 2.1.Suddenly I took out 2.1 Jquery from my code. Then ran it and was working for me well. After trying out the first answer. please check out your file like I said above.