Maria was in the front seat of the car when it was driven away, but was not in the vehicle when it was found a short time later.
The girl's father had met with an unknown man at 4.37pm on Sunday, with a view to selling his car.
The man jumped in the car and drove away, with the seller's daughter in the front passenger seat.
It was then found abandoned nearby, in Hatherway Crescent E12, but the girl was not inside.
She is Maria Tudricai, aged 17 months, a Romanian girl from the local area. She was wearing a white top and red bottoms.
She is now described as a high risk missing person, and police have urged anyone with information on her whereabouts to call 999 immediately.
The man who took the car is described as an Asian man of slim build, who was dressed in black clothing.