Feb. 6 (Bloomberg) -- Yandex NV is poised for its biggest one-day drop in a week after a report showed that the operator of Russia’s most popular Internet search engine’s market share dropped, while competitor Mail.ru Group’s increased.

Yandex’s U.S.-traded shares fell 2 percent to $21.38 by 2:08 p.m. in New York, the largest decline since Jan. 30, based on closing prices. The stock earlier tumbled as much as 3.8 percent, the biggest intraday slide since Jan. 13.

Based in The Hague, Netherlands, Yandex saw its share of the Russian search market decline to 59.3 percent in the week through Feb. 5, from 59.4 percent the previous week and below the four-week average of 59.6 percent, Liveintenet.ru, an Internet-service provider and researcher, reported today on its website. The share of Mail.ru, the largest Russian-language Internet company, rose to 9.3 percent from 9 percent in the previous week and was above a four-week average of 8.7 percent, the data showed.

“Yandex share is deteriorating and has been falling since the beginning of December, while Mail.ru has continued to gain market share,” David Ferguson and Anastasia Demidova, Moscow- based analysts at brokerage Renaissance Capital, wrote in a report e-mailed today, citing Liveinternet data. “Our preference remains Mail.ru.”

Global depositary receipts of Mail.ru rose 0.5 percent to $34.28 in London, and have climbed 32 percent this year. Yandex is trading at 37 times analysts’ earnings estimates, compared with 44 times for Mail.ru, according to data compiled by Bloomberg.

Yandex reports fourth-quarter earnings on Feb. 22 and Moscow-based Mail.ru releases its 2011 results on Feb. 24.

Google Inc.’s share of the Russian search market fell to 25.3 percent from 25.5 percent, compared with a four-week average of 25.6 percent, the Liveinternet.ru data showed.

--Editors: Marie-France Han, Emma O’Brien

To contact the reporter on this story: Halia Pavliva in New York at hpavliva@bloomberg.net

To contact the editor responsible for this story: Emma O’Brien at Eobrien6@bloomberg.net