Btw, I wouldn't say "Das Thema wächst." A topic isn't something that grows. Maybe you could use it metonymically for "thread", but I don't think I would in this context. I'd be curious to hear what other native speakers have to say on that. It's an interesting choice.
All I know is that I see "Thema" used on the German messageboards that I post on (United Schranz Board, etc.)