Greg Grimmer and Mark Waugh, the former managing partners at the agency, also become the executive directors. The changes have been made to give clients more access to senior executives.
Timlett, who joined Optimedia in 1997 from CIA, will now oversee all of Optimedia's buying operations, which encompass i-trade, the division that combines broadcast and interactive buying.
Turzynski said: "It was so easy to promote Simon and Enyi. In both cases we have been wanting to do it for years. Simon's role is designed to emphasise the value of buying, to make sure that we are fundamentally a very good buying company."
Nwosu was appointed a year ago to run village@optimedia, which offers clients solutions outside of traditional media.
Turzynski was promoted to the role of managing director two months ago, after the departure of Simon Mathews.
Turzynski added: "All the executive directors will run a quarter of the agency and will give clients access to the senior resource. Clients we talk to now are way above the level we have traditionally spoken to."