Soonthorn Areerak, channel planning director at MEC Thailand, will replace Teo as managing director for Singapore.
Teo, who will be based in Shanghai, will also split her time between the agency's Beijing and Guangzhou operations in China.
In her new role, Teo will report to David Morgan, chief executive officer, North Asia, MEC and work on MEC's Sony Ericsson, Ikea, DaimlerChrysler, Cola Cao, Remy Martin, Singapore Airlines and DHL business.
"I have been with MEC since day one when it was a CIA outfit in 1996," said Teo, who oversaw the merger of CIA Asia-Pacific and The Media Edge.
"China, already the world's fifth largest advertising market, is predicted to become the world's largest advertising market within this decade. My role at MEC China will include leveraging on the existing strengths of our office there and developing clients towards overall communications planning and implementations."
Teo added that both China, which has traditionally been a "buying-dominated market", and Singapore would see a greater focus on the agency's media-neutral channel planning and implementation offering.
MEC promotes Teo to top role in China, Areerak to S'pore
MEC has promoted its Singapore managing director Bertilla Teo to chief executive officer, MEC China.