He says the U.S. will continue its policy of not paying a government ransom, but that families have never been prosecuted for trying to pay for the release of hostages.
He tells families: "We will not abandon you. We will stand by you."
Obama's remarks at the White House on Wednesday came as he announced the results of a six-month review of hostage policies.
The review was prompted by families who complained about threats of prosecution — and about sparse, confusing and sometimes contradictory information from the government.