Mansell, who founded TBG in 2001, is seeking a raft of new senior hires including a managing director, deputy managing director and marketing director to help him run the business.
While a new position for Mansell has not been confirmed, he is likely to step up to the position of chief executive.
He said: "Due to recent growth, I have been meeting with senior candidates to help in TBG's development. I will continue to work at TBG, but want to focus on innovation, client strategy and new business."
Prior to launching TBG London, 29-year-old Mansell worked in sales at online loyalty programme MyPoints. TBG's clients include EasyCar, Unicef, Vodafone, and Moneysupermarket.com. It picked up the £3m EasyCar account from LBi last year.