The work by Karen Newman was to be submitted on April 1 to the selection panel for The Society of Portrait Sculptors annual exhibition before going on show at The Gallery in Cork Street, London.
The bronze resin portrait head was taken from the car when it was broken into in Dovedale Road in Dulwich on March 26.
This portrait, though not a commission, was made from a series of sittings with Mr Dance. It was first started by Ms Newman in 2004, but was only finished just before it was stolen. Mr Dance even came to see the portrait over the Easter weekend. It was signed in pencil as the artist intended to engrave her signature on it shortly afterwards.
Anyone with information is asked to contact PC Johnson of Southwark Police on 020 7378 1212 quoting the crime reference number 301 0914 - 08.