The account will strengthen the agency's existing relationship with the holiday company after it was appointed to its £5m advertising account in August.
Jae Hopkins, head of communications at Butlins, said: "Social media is a great way of spreading the experience that our guests enjoy at Butlins and we're looking forward to having a lot of fun with it. Now came up with some great ideas and clearly understand the brand."
Mark Lund, managing partner of Now, said: "The enjoyment of Butlins is made for sharing and we're looking forward to helping make that happen on the best sharing medium.
Butlins launched its first TV ad by Now over Christmas. The 30-second spot, called "Bounce", featured a little girl whose excitement takes the form of an irrepressible bounce after spending the day at Butlins.
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