Hi I have tried your code and it works when you do like below:
$user_id = get_current_user_id(); // this will give user id of current loged in user
// or try using this to get author ID related to your post, this will give $user_id of post author
$temp_post = get_post($post_id);
$user_id = $temp_post->post_author;
var_dump(get_the_author_meta( 'twitter', $user_id ));
similarly for other fields, please replace in your code accordingly:
get_the_author_meta('googleplus',$user_id)
get_the_author_meta('facebook',$user_id)
get_the_author_meta('linkedin',$user_id)
For details Please follow get_the_author_meta codex
For more details please follow this link get_the_author_meta developer
I think we need to pass $user_id when need to use outside the loop.
Thanks!