Additional contact fields in WordPress, display, and saving additional contact field when registering new Wordpress user. Used bootstrap for registration form part. Add this code to your functions.php

additional_contact_fields_wordpress

// Add Twitter, Facebook and Google+ field to contact methods, remove AIM, YIM and Jabber

 
add_filter( 'user_contactmethods', 'ts_add_contact_fields' );
function ts_add_contact_fields( $contactmethods ) {
  $contactmethods['linkedin'] = 'LinkedIn';
	$contactmethods['twitter'] = 'Twitter';
	$contactmethods['facebook'] = 'Facebook';
	$contactmethods['googleplus'] = 'Google+';
 
	unset( $contactmethods['yim'] );
	unset( $contactmethods['aim'] );
	unset( $contactmethods['jabber'] );
 
	return $contactmethods;
}

display_additional_fields

// Display additional contact fields in WordPress registration form

 
add_action( 'register_form', 'ts_show_extra_register_fields' );
function ts_show_extra_register_fields() { ?>


<div class="control-group">
  <label class="control-label" for="inputEmail">Username</label>
	<div class="controls">
	  <input type="text" name="user_login" placeholder="Username" id="user_login" class="input-medium" />
	</div>
</div>        
<div class="control-group">
	<label class="control-label" for="inputEmail">E-mail</label>
	<div class="controls">        
        <input type="text" name="user_email" placeholder="E-mail" id="user_email" class="input-medium"  />
    </div>
</div>        
<div class="control-group">
	<label class="control-label" for="inputEmail">LinkedIn URL</label>
	<div class="controls">        
		<input type="text" name="linkedin" placeholder="LinkedIn" id="linkedin" class="input-medium" />
    </div>
</div>    
<div class="control-group">
	<label class="control-label" for="inputEmail">Twitter</label>
	<div class="controls">        
		<div class="input-prepend">
		  <span class="add-on">@</span>		
			<input type="text" name="twitter" placeholder="Twitter" id="twitter" class="input-small" />
		</div>
    </div>
</div>    
<div class="control-group">
	<label class="control-label" for="inputEmail">Facebook URL</label>
	<div class="controls">        
		<input type="text" name="facebook" placeholder="Facebook" id="facebook" class="input-medium" />
    </div>
</div>    
<div class="control-group">
	<label class="control-label" for="inputEmail">Google+ URL</label>
	<div class="controls">        
		<input type="text" name="googleplus" placeholder="Google+" id="googleplus" class="input-medium" />
    </div>
</div>    		
<?php }

save_additional_fields

// Save additional contact fields when registering new WordPress user

 
add_action( 'user_register', 'ts_register_extra_fields', 100 );
function ts_register_extra_fields( $user_id, $password = '', $meta = array() )  {
  $userdata = array();
 
	$userdata['ID'] = $user_id;
	$userdata['twitter'] = $_POST['twitter'];
	$userdata['facebook'] = $_POST['facebook'];
	$userdata['googleplus'] = $_POST['googleplus'];
 
	$new_user_id = wp_update_user( $userdata );
}