who performed this single?
Supergroup Artists
We Are the World 25 for Haiti
"We Are the World 25 for Haiti" is a charity single recorded by the supergroup Artists for Haiti in 2010. 
who sang in we are the world haiti UNANSWERABLE what is we are the world 25? It is a charity single.
wiki:7306839
We Are the World 25 for Haiti [SEP] Introduction
"We Are the World 25 for Haiti" is a charity single recorded by the supergroup Artists for Haiti in 2010. It is a remake of the 1985 hit song "We Are the World", which was written by American musicians Michael Jackson and Lionel Richie, and was recorded by USA for Africa to benefit famine relief in Africa. Initially, in late 2009, it had been suggested to Richie and Quincy Jones—producer of the original "We Are the World"—that a re-cut version of the song be re-released under the title "Live 25". Following the magnitude 7.0 M earthquake in Haiti, which devastated the area and killed thousands of people, it was agreed that the song would be re-recorded by new artists, in the hope that it would reach a new generation and help benefit the people of Haiti.