The sculpture by Kenneth Armitage (1916-2002) was stolen on January 15 from its premises at 158-164 Fulham Road.
The auction house reported to police that according to CCTV footage a woman wearing sunglasses and a hat visited the saleroom and put the sculpture into her bag and left.
Anyone with information should contact the Met, quoting reference 5601018/24 or contact Crimestoppers anonymously on 0800555111.