Have to download facebook.php file into theme folder.
Get file from following url http://github.com/facebook/php-sdk/raw/master/src/facebook.php

<?php 
require_once('facebook.php'); 
$facebook = new Facebook(array(
'155396374496007',
'secret' => '33a5523fa4fdeecb2e5c29d55afc9627',
'cookie' => true,
));
$result = $facebook->api(array(
'method' => 'fql.query',
'query' => 'select fan_count from page where page_id = give_ur_page_ID_here;'
));
$fb_fans = $result[0]['fan_count'];
?>

To Display facebook fans Count Use Code Below

echo $fb_fans;