Yelp Inc., the San Francisco-based review website, said it was buying German company Qype, a similar European site that will help Yelp’s global expansion. The purchase price was put at $50 million. Yelp is already established in 19 countries, but the Qype acquisition will strengthen its presence in 13 European nations. More than 15 million unique visitors use the Qype service each month. “Bringing Qype into the fold will enable us to accelerate our international growth and increase our benefit to consumers and businesses,” wrote Jeremy Stoppelman, Yelp’s chief executive and cofounder, in a blog post.