O’Mara hired Shawn Vincent of Orlando’s Digital Marketing Revolution to manage a Facebook page as well. Within hours of the page going up, hundreds of people had posted comments both for and against the defendant, and a few people with fake user names shared harsh opinions of Trayvon Martin’s family. One commenter on O’Mara’s Facebook page said Trayvon’s mother was “mooching” off white people’s money.

Within 24 hours, the site was changed so that users must submit comments for review before they are posted. Insults were deleted. About 1,800 people have “liked” the page so far.

Jayne Navarre, a South Florida consultant who devises social media strategies for lawyers, said O’Mara’s use of social media will “almost certainly” taint a jury pool and compromise Zimmerman’s shot at a fair trial. She said O’Mara also may be violating American Bar Association rules that prohibit a lawyer from helping third parties make prohibited extrajudicial comments.

While use of social media has risen exponentially in the legal field, “what we have not seen is a criminal-defense attorney host social media channels on behalf of their client,” Navarre said. “I would not be surprised to learn that members of the Bar are shocked and even disgusted.”

Under American Bar Association rules, a lawyer can speak publicly on a case as long as it does not prejudice a potential jury. The association is revamping its rules to address social media, she said.

Lawyers usually use social media to advertise, educate, network or recruit employees, she said. Some lawyers and judges have been sanctioned for inappropriate use of social media.

Until now, Navarre said, the most unusual case of a law firm using social media was in 2010, when the Massachusetts-based class action firm Sokolove Law Inc. launched the first known niche social networking site devoted to engaging potential and current class members in online discussions about the birth control pill YAZ. But the site was considered advertising and was deemed in compliance with ABA rules, she said.

“The tactic certainly was cutting edge, and I don’t think the Bar saw any writing on the wall,” Navarre said. “I find in my social media consulting practice that many lawyers are still dragging their feet for various reasons . . . Others find it unprofessional, period.”