The hacker, who goes by the name Klanklannon, said he had broken into Martin’s email and Facebook account, and leaked the teen’s private messages.
The hacker said the leaked messages had been written to the politics section of an online message board for anarchists, 4chan.
Martin, 17, was killed in Florida in February after an altercation with neighbourhood watch volunteer George Zimmerman.
The death has sparked national debate and incited race hate.
Since 911 tapes were released last week, Robert Zimmerman, the brother of the alleged killer, said his family has received death threats, but he believes the “tide has turned” after initial outcry at police handling of the situation.
He said: “There’s a lot of loose ends to this story, some of them have to do with the events of that night and the investigation.
“Some of them have moved on to a lot of hate speech, people like the McClain family having to flee their home, people putting emotions ahead of fact, and putting our family, and other families, in danger.”
Meanwhile, the hacker, Klanklannon has posted slides to the 4chan website which paints Martin out to be a deviant.
One titled ‘Trayvon Martin Used Marijuana Habitually,’ features an exchange between Martin and a friend about getting high.
Another slide, ‘Trayvon Martin was a Drug Dealer’ features Facebook messages and photos that supposedly prove Martin dealt drugs, including a picture of Martin posing ‘aggressively with a large amount of cash in his hand.’
The hacker, who is known to frequent the online neo-Nazi message board, Stormfront, also posted what he said were Martin’s email and Facebook usernames and passwords, including ‘niggerniggernigger, and coontrayvonnigger’.
After posting Martin’s private messages, the hacker taunted online: “Where did all the liberals go? Did they run off because they can’t handle the facts?”
Martin’s supporters have tried to counter the smear campaign by posting emails which paint him out to be an average youth, preparing for college.
There are emails about upcoming SAT tests and scholarship applications. One email included the results of a career aptitude test, and spoke about his interest in aeronautics.
Martin’s alleged killer, Zimmerman, who claimed he had acted in self-defence, was initially arrested but released without charge.