Green’s Dictionary of Slang

(US) one who engages in necking n. (2)

1922		Appleton Post-Crescent (WI) 6 May 11/1: Flapper Dictionary heavy necker – A Biscuit, or flapper, very fond of petting. [Ibid.] 9 May 9/1: necker – A Flapper or Flipper given to cheek-to-cheek dancing.
1929		Variety 3 Apr. 20/2: Champ necker and flame of the campus falls in love with a young and good looking professor [DA].
1950		P. Highsmith Strangers on a Train (1974) 72: The island. It looked like a neckers’ paradise.
1986		L. Heinemann Paco’s Story (1987) 44: The kid steering with the necker’s knob and asking questions.