Writing to a file new line

Whenever I write to my file after the registration form and it is successful it overwrites existing data in the text document rather than adding a new line, I tried to get it working by using environment.newline but it didn't work.

' Wtites data to file.
            FileWriter.WriteLine(Userdata)
            FileWriter.Write(Environment.NewLine)
http://www.dreamincode.net/forums/index.php?app=forums&module=post&section=post&do=new_post&f=67#
            FileWriter.Close()

Sorry for the link to somewhere I don't know how that happened.