“The model has existed for a long time,” said Sven Bode, managing director of Financialright, the Hamburg-based company that owns My-right.de. “What is new is that we can do it on a massive basis.”

Mr. Bode has previously overseen efforts to help airline passengers obtain compensation for canceled or delayed flights, and to pressure banks to refund improper fees. But because Volkswagen is Europe’s largest carmaker by far, Mr. Bode said, “this is a unique dimension.”

Because the start-ups are considered collection agencies rather than law firms, they are allowed to work on commission. Clients who sign up agree to pay about a third of any money they collect, similar to contingency fees for lawyers in the United States. The Volkswagen owners owe nothing if the efforts to collect are unsuccessful.

About 100,000 Volkswagen owners have registered with My-right.de so far, said Christopher Rother, managing partner of the law firm Hausfeld in Berlin, which is working with the website. The firm’s founder, Michael Hausfeld, who is based in Washington, is one of the plaintiffs’ lawyers leading the class action against Volkswagen in the United States.

That is only about 5 percent of the eligible owners in Germany, Austria and Switzerland. Mr. Rother said the goal was to assemble at least 400,000 customers and collect up to €5,000 for each one.

Frédéric Pelouze, chief executive of Weclaim.com, the Paris-based website that is recruiting owners, said the carmaker was underestimating how vulnerable it was to new legal strategies. “The rules are changing, and I don’t think Volkswagen is getting it,” Mr. Pelouze said.