The founder of Russia's equivalent to Facebook, the social networking site VKontakte (VK), has resigned as CEO of the company after seven years, saying that he could no longer "stick to the principles" of freedom and independence.

The move was not unexpected as Pavel Durov, 29 sold his 12% holding in the firm in January to Ivan Tavrin, chief executive of Russian mobile phone operator Megafon, at an estimated value of $420 million

Megafon is co-owned by Russia's richest oligarch, Alisher Usmanov, also an ally of President Vladimir Putin, with an estimated worth of $20.2 billion.

The billionaire partly owns the internet group Mail.Ru which bought the shares from Tavrin, increasing its stake in VK to 52%.

In a statement to his VKontakte page, Durov said: "The CEO has significantly less freedom in managing the company after the changes occurred in the Vkontakte shareholders' structure in April 2013. It has become increasingly complicated to stick to the principles we once founded our social site upon."

The farewell letter included this picture:

So Long
Pavel Durov / Vkontakte

VK - previously known as VK or ВКонтакте in Russian - is the second most popular social network in Europe, with a particularly strong following in Russia, Ukraine and Belarus. It has around 200 million accounts and 45 million daily average users - compared to over one billion accounts and 665 million daily users for Facebook.

It offers very similar features to Facebook with its core functionality including photo sharing, private messaging, status updates and news sharing.

Durov, who founded the site in 2006 with his mathematician brother Nikolai, has been compared to Facebook's Mark Zuckerberg and is known as an eccentric libertarian in start-up and left-wing groups.

He was estimated to have a personal fortune of £170 million prior to selling his stake in the company, though his total net worth now will still be some way short of his US counterpart Zuckerberg who has an estimated personal wealth north of £11 billion.

In 2011, when protests against the Kremlin exploded in the streets amid allegations of election-rigging, Russian authorities demanded Durov to shut down VK pages operated by activists.

The defiant VK founder refused and responded by posting a picture of a dog wearing a hoodie to his Twitter page:

In an open letter he insisted that his decision was motivated by business rather than politics and re-affirming his neutrality. But the Kremlin started to horn in on social media and in April 2013, during a police raid on Durov's home, he was accused of driving a white Mercedes over the foot of a traffic cop.

He denied any wrongdoing but fled the country before police could arrest him. After the raid, two VK co-founders decided to sell their 48% stake to United Capital Partners (UCP), an investment firm managed by Ilya Sherbovich, who is believed to be close to Putin.

Since then, Sherbovich publicly slammed Durov's actions accusing him of using VK resources to promote the instant messenger Telegram, a Berlin-based firm that he funds.

Durov, on the other hand, became increasingly outspoken on mass surveillance and freedom of speech in Russia.

In August 2013, he invited NSA whistleblower Edward Snowden to join his team at VK.

He said he would be "happy for [Snowden] to join a stellar team of programmers" in VK's St. Petersburg office.