In his new position, Allen will work in NGN's newly created sales hub system, providing expertise in the retail sector, and will look after retail accounts across the company.
The position is Allen's third job since leaving MGN in June last year, when his role - head of newspapers - was made redundant in an overhaul of the sales department.
Within weeks, he joined The Mail on Sunday as head of magazines, covering Ella Dolphin's maternity leave, and subsequently became commercial director of upmarket property magazine So London, which folded after two issues last month.
Allen's appointment follows the departure of a number of senior sales staff at NGN after the restructure into hubs, including retail advertising manager Yvon Nolle, head of business development Sara Jubb and head of classified Tracy Gilbey.
It is understood that Nolle was offered Allen's role.
NGN previously had a separate retail unit, as well as a business development unit.
These duties are now part of the responsibilities of the three multi-platform hubs, which contain specialists from each discipline with team responsibilities split by agency.
The new structure also reflects the organisation's investment in multimedia offerings.