Police were called to the Cron Ave, Te Atatū house about 2.30am on Sunday, August 6.
Detective Sergeant Murray Free said the couple were asleep when their room was engulfed in flames.
"One person received burns to their face, and both occupants were treated for smoke inhalation and minor burns to their bodies," Free said.
"The house was extensively damaged by fire and the couple were forced to move out of their home."
Free said it was a "terrifying ordeal for the victims, and a completely unprovoked attack, which will have a financial impact on [them]".
A Molotov cocktail is a crude incendiary bomb made from a glass bottle filled with flammable liquid which is then lit before it is thrown.
Police executed a search warrant this week and arrested a 16-year-old over the incident.
"I want to reassure the community that we are committed to making sure people are held accountable for their actions," Free said.
