The girl's father, a senior state electricity board (TNEB) official, had received a phone call last night, saying his daughter was in safe custody and sought Rs 20 lakh as ransom for her release, they said.
Police tracked the calls received on mobile phone as originating from Gandhipuram in the city.
Meanwhile, a night patrol police team noticed a couple moving in a suspicious manner around 1.30 AM and they were nabbed at Avarampalayam, some distance from Gandhipuram, they said.
The girl was sent back to her parents, police said, adding, the boy, studying in a polytechnic in the city, is being further questioned in this connection.
