Donna Summer and Dionne Warwick have headbands, no idea who the woman in the white dress is. I recognize some of the singers, Christopher Cross, Kenny Loggins, James Ingram, Stevie, Lionel, Dionne and Michael.
To add from wikipedia:
Quincy Jones assembled an all-star choir for Summer's recording, including Lionel Richie, Dionne Warwick, Michael Jackson, Brenda Russell, Christopher Cross, Dyan Cannon, James Ingram, Kenny Loggins and Stevie Wonder. Jones has claimed that this song laid the foundation for the group effort "We Are The World," which was written by Jackson and Richie and was produced by Jones, who called upon many more of his famous friends for help