It isn't supported by plunker. But I tend to use http://typescript.io/ when I need third party lib support (e.g. angularjs). Otherwise I just stick with TypeScript Playground http://www.typescriptlang.org/Playground/
Update
You can use TypeScript anywhere you like using https://github.com/basarat/typescript-script (plunker sample : https://github.com/basarat/typescript-script#plunker)
That said many playgrounds now support TypeScript natively including plunkr : https://github.com/ggoodman/plunker-run-plugin/blob/master/README.md (just put "use typescript";
at the top of your file and add a tsconfig.json
file 🌹