The game has almost doubling the company's market value in just over a week.
Suddenly the mobile game had more users in the US than Twitter just one week after launch. Its players are highly engaged, spending far more time in the app than they do with some of the most popular social apps such as Instagram or WhatsApp.
The whole thing has had analysts scratching their head. Before they were happy to write off Nintendo which has not had much luck since the Wii dropped out of fashion. However it is not clear how the game can be used to boost profits.
Investors are waiting to see when Pokemon GO will be launched in other major markets, particularly Japan, one of the world's biggest gaming markets.
The game is now available in the United Kingdom and Germany after being launched in the United States, Australia and New Zealand last week.
Nintendo's shares rose to their highest level since mid-2010. At that price, the stock is up 86 percent from last Thursday, adding almost $15 billion to the company's market value.