Early on, African-Americans using social media kept the story alive, rather than the popular press. 

"The minute you get a message out there that has engagement that gets people's imaginations fired up or gets their emotions or passions stoked, it's going to go beyond your network because you may have your 130 Facebook followers but each one of them has 130 of their own so the message can spread like wild fire," said Michael Stricker, director of social media with the Internet marketing firm Webimax.

During one week, more than a million people signed an online petition and numerous messages appeared on social media sites calling for the arrest of George Zimmerman, the neighborhood crime watch volunteer who told police he shot Martin in self defense.

Even on college campuses, like Howard University in Washington, students used Twitter, Facebook and other social media outlets to communicate and even organize demonstrations.

“It hit close to home for a lot of students here because they are not much older than Trayvon Martin when he was killed. So they [the students] wanted everybody to know about this story and how they felt it was simply an injustice to a young black man,” said Ingrid Sturgis is an assistant professor of journalism at Howard University. She says young African-Americans often use social media to draw attention to social causes.

"I think it is one of the best tools today to help people get out the messages that they want to get out depending whether it is racial injustice or whether it is to support a cause," Sturgis said.

A Pew Research study says blacks use mobile phones and other devices to gain access to social media sites in larger numbers than Americans overall. 

"These conversations have always happened, but they have been in the barber shop or they have been in the drug store or they have been on the street corner. I think what is happening now is social media allows us all to see that conversation and how it has manifested in a more tangible way and it increases our awareness," said David Johnson, a journalism professor at American University in Washington. 

Social media have been used to publicize other cases involving race. And Sturgis sees the trend continuing.

"Today, you don’t have to be a part of an organization to get your voice out there. I think that social media is going to increase in the number of ways that people can get their message out and how much attention and whether or not you can make change. And I think it is going to take a greater role in doing that," Sturgis said.

Other analysts predict social media use among African-Americans will spike again when George Zimmerman, the man accused of killing Trayvon Martin, goes on trial.