For example URL would be like- http://funranger.com/Home/CardDetails/?cardID=178
you can get it like this -
@{
string encodedUrl = String.Format("http://funranger.com/Home/CardDetails/?cardID={0}/",Model.cardId);
string link = string.Format("http://www.facebook.com/sharer.php?u={0}", Url.Encode(encodedUrl));
}
Output -
Between I am confused with your usage of String.Format(), you have not mentioned placeholders any where in your String.Format() implmentation.
Also I am not sure about Url.Encode("This is my site")