Green’s Dictionary of Slang

1. (US) a promoter, a tout.

1894		Inter-Ocean (Chicago) 4 Mar. 13/3: There are at least eight men on the outside, bouncers, streeters and pluggers .
1898		Kansas City Jrnl (MO) 28 Mar. 3/2: [headline] Frank Walsh and Joe Shannon, Star pluggers Against Department Stores.
1902		Ade Forty Modern Fables 224: He had acted as a Capper and Plugger for all sorts of Shady Enterprises.
1905		H. Green Actors’ Boarding House (1906) 84: There was a fresh song-plugger with an elongated nose.
1915		Wash. Post 4 Nov. 9/5: Ellingsworth and Ruby, the ‘song-pluggers,’ will complete the bill.
1943		H.A. Smith Life in a Putty Knife Factory (1948) 131: Hanson’s drugstore operates around the clock. It is a hangout for press agents [...] song pluggers, and outcasts from café society.
1992		(con. 1956) Wolfe & Lornell Leadbelly 38: Frederick Ramsey [...] wondered if Huddie for a time was ‘a kind of song plugger on the road travelling through the South and singing current hits and contemporary songs of the early 1900’s’ .
1999		K. Sampson Powder 80: He’d bring along the sales team, pluggers, the whole mob, take them to supper, make a fuss of them.
2004		M. Wall John Peel 85: [R]ecord pluggers from indie labels were now putting their pre-release records into plain white sleeves.

2. (US Und.) in a shell game under shell n. that member of the criminal teams who poses as a bettor and appears to identify the position of the pea.

1905

Little Falls Herald (MN) 31 Mar. 3/3: How to Operate the Shell Game with Profit [...] When the steerer gets the geezer in the push, let the boosters stall until the main plugger cops.