The family of Robert Levinson, 65, who was working for the CIA as part of a rogue operation, accused the U.S. government of abandoning and betraying the missing man.
In an appearance on ABC's "This Week," Kerry said "to suggest that we abandoned him ... is simply incorrect and not helpful."
"The fact is, that I have personally raised the issue, not only at the highest level that I have been involved with, but also through other intermediaries. We don't have any meeting with anybody who has something to do with Iran or an approach to Iran where we don't talk to them about how we might be able to find not just Mr. Levinson," Kerry said.
"We're looking for proof of life, we're working on several processes that I'm not free to talk about, but there are a number of different channels that are being worked and they're being worked aggressively," he added.
Kerry said he thinks the Iranian government could help the United States find Levinson.
Levinson traveled to the Iranian island of Kish in 2007 to investigate corruption.
After he was abducted, the CIA told Congress that the agency did not have a current relationship with Levinson, and that he did not go to Iran on business.
But months later, emails surfaced that indicated that Levinson had gone to the CIA under orders from analysts who did not have the right to direct overseas operations, the Washington Post reported.
The whereabouts of Levinson remain unknown. His family last received a video and pictures of him three years ago that show him shackled and dressed in an orange jumpsuit.