Drayton, who said he has no immediate career plans, joined the performance-based online marketing group last June.
He said in a statement that he had left the Time Warner/AOL subsidiary because Advertising.com was increasingly close to its AOL parent and because founder Scott Ferber now holds the senior advertising strategy role.
AOL bought Advertising.com in 2004 for £241m. The business runs strategic direct response and brand marketing campaigns using tools such as web advertising and search listings.
Mike Peralta, UK managing director of Advertising.com, said of the forthcoming changes: "It's going to be a different structure, we are currently trying to figure it out."
Advertising.com, founded by brothers Scott and John Ferber in 1998, employs 140 staff across Europe, 85 of whom are based at its European head office in London.
The outgoing Drayton said he wanted to continue to be involved in the growth of digital. "This is a fascinating time for media businesses across Europe, especially for my particular mix of interests and experience in both digital and traditional print-based media.
"Available, affordable technology is driving consumer power and choice and shaping the future of our media and I look forward to contributing to this on-going transformation."
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