There are many 3rd party tools that will make a Sitemap from a Sitefinity site for you. One of them is XML- SiteMaps.com. To create a sitemap from their site, follow these instructions:
- Go to their website
- Complete the form on page
- Download the uncompressed sitemap, which is the first option on screen
- Upload your sitemap to your Sitefinity project (so it should be (http://www.mysite.com/sitemap.xml)
- Go to Google Webmaster Tools and either login or create an account
- Once you enter Google Sitemap, you will see navigation on the left. Click on Sitemaps
- Fill out the form to upload a Sitemap
For a complete list of 3rd party Sitemap tools, please view this webpage. For a list of Google Sitemap FAQ, please visit their site.