Sacha Dedman, 43, disappeared from her home in Plumstead in south-east London on Saturday.
Her five-year-old son, Sonny Quinlan, is also missing.
The Metropolitan Police, which is “growing increasingly concerned” for the pair, has described Ms Dedman as white and about 5ft 8in tall with long, brown hair.
Her son is described as having a dishevelled appearance, and was last seen wearing pants and a stained vest.
It is believed that Ms Dedman may be driving a white Vauxhall Corsa, with a registration of LJ14 LPA.
Anyone with any information on Ms Dedman’s whereabouts are urged to call police on 1010 quoting CAD 3253/21Sep or Missing People on 116 000.