C#: How to multithread httpwebrequests?

        /// <summary>
        /// Tests proxies for alive and Google passed.
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnTestProxies_Click(object sender, EventArgs e)
        {
            proxystested = 0;
            proxySearchPassed = 0;
            proxyTested();
            searchPassedProxy();

            this.proxyTestArray = new BackgroundWorker[this.proxyThreads];

            pr = new Structures.ProxyStruct[this.proxyThreads];

            for (int j = 0; j < this.proxyThreads; j++)
            {
                pr[j].setIP(listViewProxy.Items[j].SubItems[1].Text);
                pr[j].setPort(Convert.ToInt32(listViewProxy.Items[j].SubItems[2].Text));
                pr[j].setLanguage(this.language);
                pr[j].setProxyNo(j);
                pr[j].setHttps(chkTestProxyHttps.Checked);
                pr[j].setSocketSendTimeout(this.proxySendTimeout);
                pr[j].setSocketReceiveTimout(this.proxyReceiveTimeout);
                pr[j].setSearchTimout(this.proxySearchTimeout);

                // Set up array of objects for proxy testings
                proxyTestArray[j] = new BackgroundWorker();
                proxyTestArray[j].DoWork += new DoWorkEventHandler(aliveTest_DoWork);
                proxyTestArray[j].RunWorkerCompleted += new RunWorkerCompletedEventHandler(aliveTest_RunWorkerCompleted);
                proxyTestArray[j].ProgressChanged += new ProgressChangedEventHandler(aliveTest_ProgressChanged);
                proxyTestArray[j].WorkerReportsProgress = true;
                proxyTestArray[j].WorkerSupportsCancellation = true;
                proxyTestArray[j].RunWorkerAsync(pr[j]);
            }
        }

                    if (count != 0)
                    {
                        IP = this.listViewProxy.Items[index].SubItems[1].Text;
                        Port = Convert.ToInt32(this.listViewProxy.Items[index].SubItems[2].Text);
                        HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create(requestUriString);
                        WebProxy proxy = new WebProxy(IP, Port);
                        webRequest.Timeout = this.proxySearchTimeout;
                        webRequest.Proxy = proxy;
                        webRequest.UserAgent = usrAgent;
                    }

//your list of proxies
List<Webproxy>listProxies = loadProxies();

//used to lock so only one thread can access the list at any one time
var objLock = new object();
//used to grab the next proxy in sequence
var cntrProxy = 0;

//simple threaded parallel foreach
Parallel.Foreach(listAccounts,parallelOpts,(acc)=>{
  var proxy; 
  lock(objLock){
    if(cntrProxy>=listProxies.Count) cntrProxy=0;
    proxy=listProxies[cntrProxy];
   cntrProxy++;
  }

 //do what you want with proxy and acc

});