The use of social networking sites such as Facebook, Twitter and YouTube by militant and hate groups grew by almost 20 percent in the past year, a report by the Simon Wiesenthal Center found on Monday.

The study, using research by the center and tips from the public, found more than 11,500 social networks, websites, forums and blogs promoting violence, anti-Semitism, homophobia, hate music and “terrorism,” an increase from 10,000 last year. “The numbers are probably, at the end of the day, multiples of that,” said Rabbi Abraham Cooper, the center's associate dean who has been researching hate on the Internet since 1995. “That should be taken as a low ball figure.” Extremists also were heavily promoting online the idea of operating as so-called “lone wolves” rather than as part of a group, the human rights group named after the late Nazi hunter Simon Wiesenthal said. Cooper told a news conference examples of hate on the Internet included videos of extremists appealing for recruits and showing how to make improvised explosive devices. Online games ranged from bombing Haitian earthquake survivors to shooting illegal immigrants and gays. Facebook groups included “national kick a ginger day” and “I love curry bashing.” “While children are taught that 'sticks and stones may break your bones but words will never hurt you,' it's not always true,” Congresswoman Carolyn Maloney, from New York, told reporters. “Terrorism and intolerance start with words, but they grow into actions.”