Twitter API 1.0 is deprecated and is no longer active. With the REST 1.1 API, you need oAuth authentication to retrieve data from Twitter.
Use this instead:
<?php
require_once('TwitterAPIExchange.php'); //get it from https://github.com/J7mbo/twitter-api-php
/** Set access tokens here - see: https://dev.twitter.com/apps/ **/
$settings = array(
'oauth_access_token' => "YOUR_OAUTH_ACCESS_TOKEN",
'oauth_access_token_secret' => "YOUR_OAUTH_ACCESS_TOKEN_SECRET",
'consumer_key' => "YOUR_CONSUMER_KEY",
'consumer_secret' => "YOUR_CONSUMER_SECRET"
);
$ta_url = 'https://api.twitter.com/1.1/statuses/user_timeline.json';
$getfield = '?screen_name=REPLACE_ME';
$requestMethod = 'GET';
$twitter = new TwitterAPIExchange($settings);
$follow_count=$twitter->setGetfield($getfield)
->buildOauth($ta_url, $requestMethod)
->performRequest();
$data = json_decode($follow_count, true);
$followers_count=$data[0]['user']['followers_count'];
echo $followers_count;
?>
Parsing the XML might be easier in some cases.
Here's a solution (tested):
<?php
$xml = new SimpleXMLElement(urlencode(strip_tags('https://twitter.com/users/google.xml')), null, true);
echo "Follower count: ".$xml->followers_count;
?>
Hope this helps!