Charkin, seen above in a recent BR Video interview, joined Bebo, which was bought by AOL last year for $850m, almost two and a half years ago, in October 2006. He joined from MSN where he was head of sales for UK and Ireland.
He is to be replaced by Simon Podd, head of sales UK & Ireland at Bebo.
In an email sent to colleagues yesterday, Charkin, said: "It's been fantastic working together and I know our paths will cross over the coming years and no doubt we’ll end up working together again at some stage soon. In the immediate future I'm still at Bebo till the end of January."
During Charkin's time with Bebo the site signed a partnership with Yahoo! to handle the majority of its display advertising. While at the same time it had also begun to build an in-house sales team led by Charkin.
Kate Burns, managing director of Europe at Bebo, said: "I can confirm that Mark will leave us at the end of this month after what has been an amazing two-year journey with Bebo. He has built one of the most respected and effective online sales teams in the industry, advanced the advertising model in the social media space and ultimately helped us to grow a strong business.
"While he will be sorely missed, we are happy that he will be embarking on his next entrepreneurial challenge."
Charkin has more than a decade's experience working in the online sales industry. At MSN he oversaw its EMEA regional sales business and prior to that he was UK sales manager at Lycos.
In November, Charkin spoke to Brand Republic in a video interview at the IAB Engage 2008 conference, held in London, in which he stressed the fundamental importance of social media to UK businesses. Watch the video above.
He stressed that social media is still in its infancy in terms of its possibilities, which means it should continue to grow aggressively despite the current economic conditions.
Charkin talked about the many ways in which brands can use social media to engage with consumers, from traditional online mechanics, where brands can convey a message to a specific audience, through to more engaging marketing, including seeding applications.