Easily generate sitemaps for your Multisite network each time a user publishes a new post. Simple Sitemaps for Multisite is an easy yet incredibly effective and lightweight automatic sitemap generator for Multisite. The generator will automatically create sitemaps for every site in your network, which will then be submitted to search engines like Google and updated each time a user publishes a new post.

https://premium.wpmudev.org/project/sitemaps-and-seo-wordpress-mu-style/