Twitter is going through some growing pains as they undertake efforts to expand in Japan. According to their CEO Dick Costolo, they need to focus on recruiting a sales team to get more local ads up in the market.Twitter use in Japan has grown at an unbelievable rate and they did not plan for quite this rapid of expansion.

Twitter plans to decrease its dependance on the US market by investing in foreign markets like Japan. Aside from salespeople, Twitter also plans to hire engineers. Currently, Japan has over 30 million Twitter users and 140 million worldwide. The plan is to take the 90% US dependance down to the low 80’s by 2014.

The graph below, provided by Semiocast, shows the number of Twitter users by country as of January 31st of this year. As you can see, The US is on top, followed by Brazil, with Japan not trailing too far behind.

It sounds like Twitter is taking their mission to reduce US dependance seriously and we can probably expect them to grow both the Brazilian and Japanese markets considerably as 2012 progresses. We’ll keep you posted as changes occur.