Detective Superintendent Fiona Mallon, who is leading the Scotland Yard investigation, said: "It is important that we piece together Gemma's movements from Wednesday, February 29 until the discovery in Regent's Canal in Hackney on Tuesday.
McCluskie's family was informed that police believed the torso was hers before the formal identification.
Her brother, Tony, 35, was arrested on Wednesday on suspicion of her murder and is still being held by police.
Former EASTENDERS co-star Brooke Kinsella posted on Twitter: "Thinking of you Gemma. I am so so sorry. Despair of the world we live in sometimes. RIP darling xxx."
McCluskie starred in the soap as Kerry Skinner in 2001. She appeared in over 30 episodes. Her character arrived in Walford as a friend of Zoe Slater and the great niece of the late Ethel Skinner. She briefly dated Robbie Jackson and got him to propose to her.