threading problem-alot of invoking function simultenusly

int count = 0;
Mutex mx = new Mutex();
private void ckeckproxyvalidation(string url)
{

HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);
req.Timeout = 10000;
try
{
HttpWebResponse res = (HttpWebResponse)req.GetResponse();
string tv = res.ResponseUri.ToString();
if(tv.Contains(url) && IsSiteNameExist(url))
{
//mx.WaitOne();
count++;
//mx.ReleaseMutex();
}
}
catch
{
//mx.WaitOne();
count = count - 1 + 1;
//mx.ReleaseMutex();
}
finally
{
MessageBox.Show(count.ToString());
}
}

string[] sitefortest =
{
"http://www.megaupload.com",
"http://www.google.com",
"http://www.hotmail.com",
"http://www.yahoo.com",
"http://www.bing.com",
"http://www.youtube.com",
"http://www.facebook.com",
"http://www.islamway.com",
"http://www.mediafire.com",
"http://www.videoproxy.tv",
};

foreach (string es in sitefortest/*above array*/)
{
new Thread((ThreadStart)delegate { ckeckproxyvalidation(es); }).Start();
//ckeckproxyvalidation(es);
}