TOKYO--Mixi, the Japanese social network that counts 27m users, has called in new PR support as it attempts to stem customer defection to Facebook and Twitter.

The Holmes Report understands that Burson-Marsteller has been appointed to handle corporate communications for the social networking platform, following a multi-agency review. The brief, worth around $250k per year, was previously handled by Ozma.

While Mixi remains Japan’s largest social networking site, recent growth has been outstripped by competitors such as Facebook, which has reached 10m users after doubling in size over the past six months. Mixi’s user base is considerably larger than Facebook, but Nielsen data indicates that the US website attracted more unique visitors over the past year.

Similarly, Twitter usage has grown swiftly in Japan, with Comscore reporting that the site had overtaken Mixi. Both Twitter and Facebook have seen expansion since last year’s tsunami and nuclear crisis, when their services were used extensively to disseminate information and assist in rescue efforts.

The foreign sites have also benefited from the patronage of high-profile celebrity users, which has helped to nullify one of Mixi’s unique local advantages - users can adopt pseudonyms. Mixi’s local rivals include social gaming platforms such as Gree and Mobage.

Reports last month indicated that Mixi is considering putting itself up for sale, following flat revenue growth and a 46 percent decline in profits last year.

Japan is the world’s fourth-largest internet market, with 101m users representing a penetration rate of around 80 percent. However, less than two-thirds of these users visit social media sites, despite a mobile market that is often considered the world’s most advanced.

Representatives from Burson-Marsteller did not respond to request for comment, while calls to Mixi were not returned as this story went live.