Return a list of posts by a specific author no matter the site on the multisite network

author-network-posts.php

/**
*
*	Return a list of posts by a specific author no matter the site on the multisite network
*
*	@param $userid int id of a user
*	@param $limit int number of results to return
*
*
*/
function get_user_posts_on_network( $userid = 0, $limit = 9 ) {

	if ( empty( $userid ) )
		return;

	$blogs = get_blogs_of_user( $userid );

	$out = '';

	if ( $blogs ):

		foreach ( $blogs as $blog ) {

			switch_to_blog( $blog->userblog_id );

			$posts = get_posts( array('posts_per_page' => $limit, 'author' => $userid ) );

			if ( $posts ) :

				foreach ($posts as $key => $post) {

					setup_postdata( $post );

					$out .= $post->post_title;
				}
				wp_reset_postdata();

			endif;

    		restore_current_blog();
		}

	endif;

	return $out;
}