"As technology develops, as the world moves on, we should try to avoid the safe havens that could otherwise be created for terrorists to talk to each other," Cameron said.
Messaging services like Snapchat make it difficult for authorities to track communications. The prime minister previously indicated British authorities might want to crack down on such encrypted communications.
"Because this is a whole new world ... the laws that might have been designed for the traditional wiretap have to be updated," Obama said.
The president said during the news conference that "social media and the Internet" are the "primary ways" way terrorist organizations are communicating.
Still, Obama said that U.S. authorities maintain a framework for respecting privacy rights.
"For the most part, those who are worried about Big Brother sometimes obscure or deliberately ignore all the legal safeguards that have been put in place to assure people's privacy and make sure that government is not abusing these powers."
Coinciding with Cameron's visit, the U.S. and U.K announced that they will be holding cyber war games later this year that include simulated attacks on financial institutions.
Beyond the digital realm, fighting terrorism remains a chief concern for the two countries—especially in light of the recent attacks by extremists in Paris.
"We will do everything in our power to help France seek the justice that is needed," Obama said Friday.
The two leaders spoke with the media from Washington after a morning meeting on a wide range of topics.
The White House had said the discussion covered economics, cybersecurity, terrorism, Ebola, Russian involvement in Ukraine and more.
Economic growth is also a key issue for the two nations—both of which have seen some gains on that front amid a tepid global environment.
Friday's was the 12th official meeting of the two national leaders.