The 22-year-old's single 'Tik Tok' holds on to the top spot for a ninth consecutive week.
Over 80 artists including Barbra Streisand, Pink, Kanye West and Miley Cyrus teamed up to record 'We Are The World', which was first written by Michael Jackson and Lionel Richie to raise funds for Africa relief in 1985.
The original version debuted at number 21 and rose to the top spot three weeks later.
Black Eyed Peas fall one place to number three with 'Imma Be', while Young Money and Lady GaGa hold steady in fourth and fifth place.
Jason Derulo's second single 'In My Head' climbs two places into the Top 10 and Ke$ha rises to number 11 with latest release 'Blah Blah Blah'.
Elsewhere, The Script continue a steady climb up the chart with 'Breakeven'. The track, which was released in the US in August 2009, climbs twelve places to a new peak of 28.
The second highest new entry comes from Iyaz's 'Solo' at number 43, while Rihanna debuts at 64 with 'Rude Boy'.
The top ten singles in full (click for our reviews):
1. (1) Ke$ha: 'Tik Tok'
2. (-) Artists For Haiti: 'We Are The World 25: For Haiti'
3. (2) Black Eyed Peas: 'Imma Be'
4. (4) Young Money: 'BedRock'
5. (5) Lady GaGa: 'Bad Romance'
6. (3) Lady Antebellum: 'Need You Now'
7. (7) Train: 'Hey, Soul Sister'
8. (8) Ludacris: 'How Low'
9. (11) Jason Derulo: 'In My Head'
10. (6) David Guetta ft. Akon: 'Sexy Bitch'