Async await tcp server

AsyncTcpServer

public class AsyncServer {
    private const int BufferSize = 4096;
    private static bool ServerRunning = true;       
    private List<TcpClient> clients = new List<TcpClient>();
    private PRMasterAutomation automation;

    public AsyncServer()
    {            
        InitializeComponent();
        automation = new PRMasterAutomation();
        automation.OnMonitoringEvent += automation_OnMonitoringEvent;

        if (!automation.Login("ADMIN", "")) 
            return;            

        if (automation.GetPRMasterState() == PRMasterStateEnum.StateIdle)
            automation.StartMonitoring();

        var tcpServer = new TcpListener(IPAddress.Any, 9001);
        tcpServer.Start();
        ListenForClients(tcpServer);                       
    }

    private async void ListenForClients(TcpListener tcpServer)
    {
        while (ServerRunning)
        {
            TcpClient tcpClient = await tcpServer.AcceptTcpClientAsync();
            clients.Add(tcpClient);
            ProcessClient(tcpClient);
        }
    }

    private async void ProcessClient(TcpClient tcpClient)
    {
        var stream = tcpClient.GetStream();
        var buffer = new byte[BufferSize];
        int amountRead;
        string xml;
        while (ServerRunning)            
        {
            if ((amountRead = await stream.ReadAsync(buffer, 0, BufferSize)) > 0)
            {
                var message = Encoding.ASCII.GetString(buffer, 0, amountRead);
                xml = "";
                if (message.Equals("get_users"))
                {
                    xml = automation.GetUsersXml();                                               
                }
                else if (message.Equals("get_events"))
                {
                    xml = automation.GetEventsHistoryXml("");
                }

                if (xml.Length > 0)
                {
                    xml += "\r\n"; 
                    await stream.WriteAsync(Encoding.ASCII.GetBytes(xml), 0, xml.Length);
                }
            }
        }
    }

    async void automation_OnMonitoringEvent(DateTime date, DateTime time, int networkID, int readerID, int userID, int groupID, int eventCode, int zoneID, int TandAID, string strEvent, string strAccessPoint, string strUserSource, string strGroup, string strNetwork, string strZone, string strTandAMode)
    {
        foreach (var c in clients)
        {
            if (c != null && c.Connected)
            {
                var stream = c.GetStream();
                StringBuilder sb = new StringBuilder();
                sb.Append(date.ToString() + ";" + time.ToString() + ";" + networkID.ToString() + ";" + userID.ToString() + "\r\n");
                await stream.WriteAsync(Encoding.ASCII.GetBytes(sb.ToString()), 0, sb.Length);
            }   
        }            
    }
}