Odnoklassniki has announced the opening of its 100 millionth account last weekend, reported news agency RIA Novosti. The social network now counts 71 million activated accounts – those accounts for which users have provided a valid mobile phone number.

Vkontakte.ru, the leading network, claims over 118 million user accounts and 99 million activated accounts.

Odnoklassniki’s audience is still growing but the site lost its second place ranking in terms of traffic in 2010. Last April, according to TNS, Odnoklassniki reached 18.35 million unique users aged 12 to 54 living in Russia. Based on the same criteria, the users of Vkontakte and MoiMir – another online social network – numbered 23.49 million and 19.34 million respectively.

With just 5 million active users in Russia, Facebook still lags far behind.

While Vkontakte is especially popular among users aged 15 to 25, Odnoklassniki – originally designed to reunite former classmates – has its strongest positions among those aged 25 to 35.

These social networks are all linked to Mail.ru Group, the prominent LSE listed Russian Internet group. But while the group owns a controlling stake in Odnoklassniki and MoiMir, it owns just 32.5% of Vkontakte.