here try this out
string sUsername = "NAME HERE";
string sUrl = "https://api.twitch.tv/kraken/streams/" + sUsername;
HttpWebRequest wRequest = (HttpWebRequest)HttpWebRequest.Create(sUrl);
wRequest.ContentType = "application/json";
wRequest.Accept = "application/vnd.twitchtv.v3+json";
wRequest.Method = "GET";
dynamic wResponse = wRequest.GetResponse().GetResponseStream();
StreamReader reader = new StreamReader(wResponse);
dynamic res = reader.ReadToEnd();
reader.Close();
wResponse.Close();
if (res.Contains("display_name")) {
//user is live
} else {
//user is not live
}