Social media sites such as LinkedIn and Twitter are redefining the way businesses reach their customers, but securities firms are largely absent from the revolution.

Regulators and company rules at brokerages have slowed the adoption of social media by the financial services industry, said Margaret Paradis, a partner at law firm Baker & McKenzie, who advises brokers and fund managers.

Firms banning employees from using sites such as Facebook, LinkedIn and Twitter are limiting access to cheap and easy-to-use competitive tools, she said.

Firms such as Bank of America’s Merrill Lynch and TD Ameritrade generally restrict all broker-to-investor interaction on social media sites because of concerns they may violate SEC rules and those of the Financial Industry Regulatory Authority, the body that oversees almost 5,000 brokerages.

Brokers who break the rules may be fined or suspended for communicating in a manner that’s viewed as intentionally or recklessly misleading, Finra said.

Finra requires companies to supervise and store all broker-client exchanges, including e-mails and now Twitter posts and Facebook updates.

“Networks and referrals are how this business is done, said Stacey Haefele, president and CEO of wealth marketing firm HNW Inc.

“By ignoring social media, you risk not being out there where your clients are.”

About 84 percent of US brokerage firm employees polled by HNW said they don’t use social media because company and industry regulations make it too burdensome, she said.

The Securities and Exchange Commission, which regulates the securities industry, says all broker stock recommendations must be “suitable” for individual clients by measuring their risk tolerance, security holdings, income, net worth and investment objectives, according to the agency’s Web site.

Brokerages also are required to approve most postings on Web sites, Tom Pappas, vice president of advertising regulation at Finra, said.