THE public is being asked to help find a baby girl missing after the suicide of her mother late last month. The baby was believed to have been with 24-year-old Li Wai-sum, who plunged five floors to her death in Ngau Tau Kok on July 27, Detective Inspector Tsui Sau-king said. ''She was seen leaving her North Point flat with her new-born daughter earlier in the day. ''She then went to a relative's flat in Western where she was later found to have left a suicide note in the letter box indicating that she was suffering from post-natal depression. ''She also said she had difficulties looking after the baby,'' Ms Tsui said. ''We don't know what happened to the baby girl, weighing about 2.5 kilograms and wrapped in a light purple towel, and the rucksack containing the woman's personal belongings and identity card,'' she said. The police hotline is 527-7177.