The agency, which now counts Adidas, Absolut, General Motors and Beats by Dre as clients, launched initially in the UK in 2009. The New York office was established in 2012, and Reeve moved full time to the US in 2014. The NY office had 14 staff as of the start of the year.
Reeves left the firm at the end of last week, according to a spokeswoman for the firm, to "pursue other opportunities", but added she could not confirm what.
Reeves himself told PRWeek UK he had no comment to make.
The NY office will now be led by Jilly Gray, who joined the agency in 2015 from UK creative agency Holler as digital director.
Meanwhile, the UK office will welcome James Wilkins as creative director next week, becoming the second most senior member of London staff after MD Rosie Holden.
Wilkins was co-founder of creative and digital agency Abundant in 2010, and remained with the firm after its acquisition by Way To Blue in 2014. During his tenure, he led the agency's creative strategy and established the its creative studio, working across a wide range of consumer and entertainment clients.
Holden said of Wilkins' arrival: "We look forward to some fresh thinking and a new chapter in the John Doe story."