Starting in October, social media companies operating in Germany could face fines as high as 50 million euros, or nearly $59 million, if they do not respond to requests to remove illegal, racist or slanderous comments and posts within 24 hours of being notified.

“I can’t see how Twitter is going to be able to do that,” Mr. Shapira said. More than two days after his video was posted online, and weeks after he first reported the offending tweets, many of the messages remain on the site, he said. Others, however, have either been blocked in Germany or been removed entirely.

Image Mr. Shapira. Credit... Shahak Shapira

With Twitter increasingly seen as a virtual free public space, Mr. Shapira’s actions and Germany’s new law have raised questions surrounding the role of private companies and to what extent they alone should be responsible for policing hate speech.

This question is particularly thorny in Germany, home to some of the most stringent anti-hate-speech laws in the Western world, and where the interplay between freedom of expression and the rule of the law is influenced by the country’s complicated history with both Nazism and Communism.

Mr. Shapira said he also reported about 150 similar examples of hate on Facebook, 80 percent of which were removed within three days, he said.

In its statement, Twitter stressed its policy of notifying users of the status of requests to remove hateful content. But Mr. Shapira said he had been left in the dark about many of his requests.