The trio join familiar names such as WPP founder and chief executive Sir Martin Sorrell, and Ogilvy & Mather chief executive Annette King.
Ahmed co-founded AKQA in 1994 with James Hilton when they were both 21 years old, while McEttrick became group brand director at Tesco in 2015. Valoti, a former Facebook executive, was appointed by Snapchat as UK general manager at the end of 2016.
Johnny Hornby, the founding partner of CHI & Partners, is again among the 500, as is James Murphy, the co-founder and chief executive of Adam & Eve/DDB.
Representing media agencies again are Karen Blackett, the chairman of MediaCom, and Lindsay Pattison, the global chief executive of Maxus.
Nicola Mendelsohn, the vice-president EMEA at Facebook, makes the list on the digital and social category, as does Matt Brittin, the EMEA president of business and operations at Google, and Martha-Lane Fox, the co-founder of Lastminute.com.
Sarah Wood, the chief executive of ad tech company Unruly, is also on the list in the entrepreneurs category.