The company is looking for a network to handle its media in the UK, Italy, Germany, Belgium and the Netherlands.
Billetts is co-ordinating the process and agencies have been contacted with requests for information.
In the UK, Manning Gottlieb OMD handles the account, which covers attractions including Madame Tussauds and the theme parks Chessington World of Adventures, Alton Towers, Legoland and Thorpe Park.
Last year, Merlin Entertainment spent £4 million in the UK on media but agency sources suggest its budget is likely to increase to more than £7 million as the company acquires new attractions.
Merlin recently bought the London Aquarium and owns Heide Park, a theme park in Germany, and Gardaland, the leading theme park in Italy.
Last year, Merlin Entertainment, which is owned by the private equity group Blackstone, relaunched Alton Towers with an ad campaign by Delaney Lund Knox Warren.
This article was first published on campaignlive.co.uk