The singing stars, as well as others including Myleene Klass and Alison Moyet, are rallying their followers to find 1,000 users who are willing to raise $80 (£50) each in aid of Britain's Comic Relief organisation.
Allen, who is also known by her married name of Lily Rose Cooper, is determined to beat her rivals in the contest, and has taken to her Twitter.com page to appeal for fans to join her team.
In a series of posts, she writes, "Ok so Comic Relief is upon us and I have put myself up as a Twitter million team leader. If you think you can raise £50 and let me take credit, then I'd be ver (very) grateful. Please help. I can't bear losing. And it's for charidee (sic)."
Comic Relief's Tv fundraiser Red Nose Day, which is staged to raise money for good causes, takes place on 15 March (13).