MenuItem.NavigateUrl appending to URL instead of redirecting

Question

Here is my c#;

string myUrl = "www.facebook.com"
menuItem1.NavigateUrl = myUrl;

here is my markup

<asp:Menu ID="Menu" runat="server">
</asp:menu>

But when I click the menu item, it appends to the url and does not redirect

I get ;

http://domain.com#http://domain.com/www.facebook.com

When I expect it to just redirect. Can anyone point out my , maybe obvious mistake?