Teddy Hanssen is a character who is a part of Viral Marketing Campaign for Cloverfield. He has a sister named Aylse Hanssen, who is currently searching for his whereabouts.
While it is not explicitly stated, it can be confidently surmised from the "Jamie and Teddy" videos and a visit to the website of "eco-terror group" T.I.D.O. Wave that, in addition to being Jamie Lascano's boyfriend, Teddy was an undercover operative of T.I.D.O. Wave, sent to the Chuai Station drilling platform to carry out duties related to an unspecified "event" planned by T.I.D.O. Wave to further their cause against Tagruato. A cause is mentioned both on the T.I.D.O. Wave website and by Jamie in one of her early videos to Teddy.
As heard in the audio message he sent to Jamie Lascano, which she believed was a disingenuous way of breaking up with her, Teddy Hanssen was captured prior to his being able to take part in the T.I.D.O. Wave operation on Chuai Station. If the audio message to Jamie can be trusted, we can safely assume -- given the footage of the attack against Chuai station -- that Teddy Hanssen perished when the Monster attacked Chuai Station prior to its appearance in New York City and the catastrophic events of May 22-23.
Recent speculations have pointed out that Teddy may have survived and got to New York on the Tagruato Oil Tanker, though there is no evidence to suggest the man seen on the Brooklyn Bridge is Teddy Hanssen.