Do you have some numbers+sources? I live in Germany and the official statement from the police seems to be that it is not actually a huge problem.
Also, https://en.wikipedia.org/wiki/Human_trafficking_in_Germany links to a US Trafficking in Persons Report 2010. Here are some quotes:
"Ninety percent of identified victims of trafficking for commercial sexual exploitation came from Europe, including 28 percent from Germany ..."
"... approximately one third of identified sex trafficking victims reported that they had agreed initially to engage in prostitution."
"Police estimate that gangs brought around 1,000 Chinese people to Germany over the past decade and forced them to work in restaurants under exploitative conditions."