"In the days following my release Sunday, I have learned bit-by-bit that there have been literally hundreds of brave, determined, big-hearted people all over the world worked for my release," Peter Theo Curtis said in a brief statement.
Curtis, who is now at his family home in Cambridge, Massachusetts, said he was "overwhelmed with emotion" and asked for privacy to reconnect with loved ones.
Curtis, 45, arrived in the US on Tuesday.
His mother, Nancy Curtis, said on Sunday that the Qatari government negotiated to secure his release on humanitarian grounds and expressed her "deep gratitude" to the US and Qatari officials and other individuals, both public and private, who helped negotiate her son's release.
Curtis' life was considered to be in danger after another US journalist, James Foley, had been decapitated last week by the Islamic State militants. Foley had been abducted almost two years ago.