"Social media continues to be a vital channel for brands looking to establish meaningful connections with their consumers; they are able to activate and enhance data and insights through content and media," said Gonzalez. "I'm excited to lead a network that emphasizes the importance of both innovation and performance to maximize social media investments for clients."

Duax joins MDC Partners from WPP, where he most recently served as talent director of Asia Pacific and was responsible for senior executive recruitment across WPP's company holdings and teams in Singapore, Shanghai, Sydney and Tokyo. Prior to moving overseas, he worked for WPP in New York and oversaw senior executive recruitment across WPP's firms in North America.

"No industry is more dependent on talent than ours, and we are highly proactive in ensuring that MDC and its agencies attract the very best, most entrepreneurial and most creative talent in the world," said Kauffman. "With the addition of Randy to our team, we are further enhancing our talent expertise to meet the expanding needs of our agency partners and their clients, ensuring that MDC remains 'The Place Where Great Talent Lives.'"

Prior to MMC, Vienne spent more than 17 years as a global business consultant, working with consulting firms, such as Deloitte Consulting, PwC and Ketchum Change to deliver strategic change and talent management programs. Clients included PepsiCo, United Technologies, Exxon/Mobil, Nielsen, Scholastic, Prudential Financial, IBM and HarperCollins Publishers.

"We are thrilled to have Diana join the Havas family. Diana is an incredibly talented leader who not only brings a wealth of strategic consulting and agency experience, but truly understands what it takes to win the war on talent in today's extremely competitive and rapidly changing marketplace," said Maness. "She brings an entrepreneurial mindset and infectious energy that will enable us to innovate and implement new talent initiatives across the New York Group."

"The opportunity to build a modern media department from the ground up within a smart, successful creative agency is what drew me to the role at Walrus," said Stern. "This move signals the direction our industry is headed and the solutions needed to address a complex, fragmented media landscape."

Prior to Leo Burnett, Costello spent seven years at Arnold Boston as an art director and an associate creative director, working on ESPN, Carnival Cruise Lines, Celebrity Cruises, Volvo, McDonald's and the "truth" anti-smoking campaign.

"Throughout his career, Mike has created edgy work that touches culture, from the 'truth' campaign to 'Van Gogh BnB,'" said Margaret Johnson, partner and chief creative officer at Goodby Silverstein & Partners. "This is the kind of work we admire and look forward to seeing more of with his arrival."