Club 18-30 has briefed Saatchi & Saatchi to develop a brand strategy.
It is also seeking ideas from other agencies with a view to making the concept appeal to "a more sophisticated and self-assured youth market", according to Ian Ailles, managing director for Thomas Cook's specialist businesses.
Thomas Cook declined to give details of the brand review, but a spokesman admitted Club 18-30 "had to move with the times".
A spokesman for Saatchi & Saatchi confirmed the agency was working with Club 18-30 marketers "on how to push the brand forward". He said a fresh strategy would emerge by the end of the year.
In the immediate aftermath of stories in the media about holiday-makers' misbehaviour last year - including the arrest of three Club 18-30 reps for organising illegal bar crawls - Thomas Cook chief executive Manny Fontenla-Novoa said the brand had "reached maturity" and warned about the "fine but crucial line between fun and unacceptable behaviour".
Ironically, Club 18-30 sales, which Thomas Cook does not make public, are said to have increased since last summer's negative publicity, although it is not considered to be one of the company's more profitable brands.