As part of a repositioning of the brand, the utility provider is seeking advice on brand strategy and sponsorship. The appointed agency may also be expected to advise on potential sporting tie-ins for the brand.
The move coincides with news that NPower's three-year, £21m deal with the Football League is set to end.
NPower PR campaigns manager Zoe Melarkey said: 'We are engaged in a bigger process of looking at putting customers at the heart of the business, and defining the core of our brand.
'We want to focus on our sponsorship strategy moving forward and are looking for agencies to come back to us with top-line thoughts around this.'
The hunt is understood to be part of a review overseen by Debbie Briton, who has joined NPower from AXA to oversee marketing.
However, Melarkey denied that a firm decision had been made about ending sponsorship of the Football League.