If you want text to appear inside the Visual Studio Output window, Diagnostics::Debug::WriteLine does the trick. Otherwise, use Console:WriteLine (which you seem to be using).
Looking at your code, you've got two problems.
1. You aren't reading anything from the serial port.
2. You're calling Console::ReadLine which blocks.
The easiest thing would be to create a separate thread to deal with the serial port.
QueueUserWorkItem will do here.
http://msdn.microsoft.com/en-us/library/kbf0f1ct%28v=vs.110%29.aspx[
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Code your worker thread to exit when some boolean variable has been set (or cleared).
The main thread can set/clear this flag when the program is ready to exit.
You'll need to figure out a way for the main console thread and the serial port thread to exchange data.