Green’s Dictionary of Slang

(Filipino) a young male prostitute.

1963		J. Kirkup Tropic Temper 70: Bevies of ‘billy-boys’ parade and undulate arm-in-arm along the road to the station and Jalan Mountbatten, which they refer to as ‘the street for meeting foreigners’ [Simes:DLSS].
1987		P.W. Mathews Male Prostitution 9: The clients of billyboys consist mainly of tourists from various industrialized countries, in which homosexuality is illegal or boys are not readily available [Simes:DLSS].