You might as well try posting on any job boards, freelance sites or those sites that target German writers alone. That way you'll get more results than waiting for someone who'll respond in your post. (Just a suggestion though)
It's free to post a job ad on any freelance site by the way. And it's easy to sift which applicant you think is the best among rest because they have their own recruiters who will help you do the interview.
Among the best online marketplace for freelancers, Odesk and Staff.com are definitely a worth it site to try.
Odesk is focusing on contract jobs while Staff.com is doing on both, full time and part time hires.