Add a search toggle after the regular menu items.

genius_add_search_toggle.php

function genius_add_search_toggle ( $items, $args ) {
	if ( $args->theme_location == 'social') {
		$items .= '<li id="search-toggle" class="menu-item"><a href="#"><span class="screen-reader-text">Search Toggle</span></a></li>';
	}
	return $items;
}
add_filter( 'wp_nav_menu_items', 'genius_add_search_toggle', 10, 2 );