If using the site map module via site settings -> site map and you've added to a page you'll need to insert a fresh copy each time you add new pages within the site.
The other site map that is available to you is the sitemap.xml which is enable once you enable SEO for the site. This will update automatically whenever pages are added that you can use to submit to any major search engine. "yoursite.com/sitemap.xml"
You can enable this via "yoursite.com/AdminConsole/#!/Utilities/SEO.aspx"