How to append string to the requested URL from controller action method in mvc4

Assuming I understood your problem correctly, here's the solution I propose:

Add the following change to your routing mechanism:

public class RouteConfig
{
    public static void RegisterRoutes(RouteCollection routes)
    {
        routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

        routes.MapRoute(
            name: "Tutorials",
            url: "Tutorials/{id}/{title}",
            defaults: new { controller = "Tutorials", action = "Show", title = UrlParameter.Optional },
            constraints: new { id = @"\d+" }
        );

        routes.MapRoute(
            name: "Default",
            url: "{controller}/{action}/{id}",
            defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
        );
    }
}

and then in your Tutorials controller:

public class TutorialsController : Controller
{
    // GET: /Tutorials

    public ActionResult Index()
    {
        // here you can display a list of the most recent tutorials or whatever
        return View();
    }

    // GET: /Tutorials/1 (will be redirected to the one below)
    // GET: /Tutorials/1/Intro-into-ASP_NET-MVC

    public ActionResult Show(int id, string title)
    {
        string key = string.Format("tutorial-{0}", id.ToString());
        Tutorial model = TempData[key] as Tutorial;

        // if this is not a redirect
        if ( model == null )
        {
            model = GetTutorial(id);
        }

        // sanitize title parameter
        string urlParam = model.Title.Replace(' ', '-');
        // apparently IIS assumes that you are requesting a resource if your url contains '.'
        urlParam = urlParam.Replace('.', '_');
        // encode special characters like '\', '/', '>', '<', '&', etc.
        urlParam = Url.Encode(urlParam);

        // this handles the case when title is null or simply wrong
        if ( !urlParam.Equals(title) )
        {
            TempData[key] = model;
            return RedirectToAction("Show", new { id = id, title = urlParam });
        }

        return View(model);
    }

    private Tutorial GetTutorial(int id)
    {
        // grab actual data from your database
        Tutorial tutorial = new Tutorial { Id = 1, Title = "Intro into ASP.NET MVC" };
        return tutorial;
    }
}

UPDATE:

the solution presented above will redirect
/Tutorials/1
to
/Tutorials/1/Intro-into-ASP_NET-MVC.

If you actually want to display the action name in the url, like /Tutorials/Show/1/Intro-into-ASP_NET-MVC you can just change the "url" in the "Tutorials" route to url: "Tutorials/Show/{id}/{title}".

You can also replace the RedirectToAction with RedirectToRoute("Default", new { id = id, title = urlParam }); which will make sure it matches the route named "Default", but this approach would yield the following url: www.mysite.com/Tutorials/Show/1?title=Intro-into-ASP_NET-MVC