There's no continous form in German, so you either use an appropriate adverb (e.g. "gerade"), or you just use the normal non-continous form:
Ich lerne Deutsch (implies that you've been learning it for a while, and still doing it)
Ich arbeite gerade an einem großen Projekt (right now, I'm working ...)
Ich investiere Geld in Twitter-Aktien. (of course you're doing it right now, otherwise you'd have used Perfekt or Imperfekt)