Nassau County officials are encouraging social media users to take screenshots of suspicious online threats, including chatter about ISIS and other possible terrorist activity, and report them to police through a cellphone app.

County Executive Edward Mangano launched the “See Something, Say Something” counterterrorism initiative Tuesday at a news conference in Mineola.

The program encourages users of social media sites such as Facebook and Twitter to text a tip, such as a suspicious package or an individual declaring their allegiance to a known terrorist group, through the free Nassau CrimeStoppers app.

“This is in essence a modern-day Civil Defense, which has the potential to thwart attacks,” said Mangano, referring to a 1941 program in which President Franklin D. Roosevelt urged Americans to watch for espionage and sabotage.

Acting Nassau Police Commissioner Thomas Krumpter said tips will be vetted by the department and then forwarded to the Asset Forfeiture and Intelligence Unit.

“If they see some radicalized views or threats on Facebook, don’t assume that we know about it,” Krumpter said. “If you see somebody with radicalized views talking about a terrorist attack, talking about blowing something up, we want to know about those.”

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Jason Starr, director of Nassau’s New York Civil Liberties Union chapter, said monitoring an individual strictly for their beliefs — however unpopular — could have a “chilling effect” on free speech.

“That’s why we have a First Amendment,” Starr said. “It is not illegal to identify with an idea, even if it’s troubling or problematic. You combat that idea with even more speech.”

Det. Sgt. Patrick Ryder, commanding officer of the Asset Forfeiture and Intelligence Unit, said 20 civilian department analysts spend at least one hour per day mining information on social media looking for potential threats.

“And then we can go into these communities and pull out those that may have extreme views,” Ryder said.

Tips are anonymous. If the information leads to an arrest or conviction, tipsters could receive a reward of up to $5,000.