Credited with implementing the association’s post-merger reorganisation from February 2010, Riess left at the end of March.
A spokesman said he had “fulfilled his assigned role to the expectations of WAN-Ifra”, turning around its previously negative financial position.
“He has done well and we are grateful to him for his services and wish him all success in the future,” president Jacob Mathew said.
The three deputy chief executives – supported by chief financial officer Andreas Musielak – will function as executive management, with Werfel, who is the most senior, acting as interim chief executive.
Based in France and Germany, with subsidiaries in Singapore, India, Spain, France and Sweden, represents more than 18,000 publications, 15,000 online sites and over 3000 companies in more than 120 countries. Its core mission is to defend and promote press freedom, quality journalism and editorial integrity and the development of prosperous businesses.