Katie,
This sounds like a valuable piece of porcelaine.
The TK Thuny mark on the reverse of your serving platter dates it as pre 1945.
The "Thun" factory used this marking from 1819. I am afraid without seeing the plate in detail, I cannot give further information.
You have not indicated what condition your platter is in.
I would be most interested in both seeing it and finding out in what condition it
remains.
Are you considering offering the serving platter for sale?
Yours faithfully
Khalil Khalem