Met Police officers are still trying to trace William Deo, 20, and Gavin Okwu-Brewis, 29, following the attack in Ilford, east London, on Wednesday 13 June.
A man in his 20s was left in a critical condition with serious injuries after having what police described as a noxious substance thrown at him.
Officers said the substance is believed to have been ammonia.
The force issued its latest warning as it confirmed a 19-year-old woman had been charged in connection with the attack.
Makayla Hajaig, of Barley Lane, Chadwell Heath, has been charged with robbery, grievous bodily harm with intent and actual bodily harm, and is due to appear at Barkingside Magistrates’ Court today.
In a statement, police said: “Inquiries continue to trace two men, William Deo, 20, and Gavin Okwu-Brewis, 29, in connection with this offence.
“They should not be approached.”
:: Anyone with information about the men is asked to call police on 999, quoting reference 8771/13 June.