Placing a url in a search textbox

Hi i have a textbox in which users can type a value they want to perform a search on, the textbox also accepts url's, however i am getting a resource not found when a url is typed into the textbox. This never happens when it is  just a word. For instance if
http://www.google.com is typed into the box i get a resource not found, it seems like the page is trying to redirect to it. Here is my search button method;
Response.Redirect("~/Admin/Site/results.aspx?searchvalue=" + "/" + strSearchText + "/");


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