The rapid expansion has fueled speculation that some of the tech firms could either be bought by larger United States rivals that want to expand globally or potentially become public companies through multibillion-dollar initial public offerings.

“Rocket has disrupted the entire venture capital industry,” said Christophe F. Maire, a leading Berlin-based investor who has backed several of the city’s best-known start-ups, though none from Rocket Internet. “It has groomed a lot of people in the art of going international.”

But the success has also raised questions about the value of a company that essentially depends on the ideas of others. Although the Rocket-supported companies are free to copy existing tech businesses as long as they do not infringe on copyrights and trademarks, there is nothing to stop competitors from rising up and pursuing the same strategy. And some companies have already popped up to parrot Rocket’s business model.

While the company has created a growing stable of global e-commerce start-ups, it has had less success with other Internet businesses. The company’s version of Pinterest, for example, which allows people to share photographs and other media, has so far failed to win over many consumers.

And after Airbnb held talks in 2011 about acquiring Rocket’s Berlin-based copy, the American short-term housing website eventually decided to beef up its own international operations instead of buying the smaller rival.

Others in the tech industry question whether Rocket Internet can maintain its success rate, as start-ups from Silicon Valley to Singapore look to expand globally as quickly as possible. That could cut the time Rocket Internet has to replicate successful tech ideas in emerging economies and other non-American markets.

“Just copying what the Americans have done is no longer a sustainable model,” said Simon Cook, chief executive of the European venture firm DFJ Espirit.