Some ads for animated shorts that ran in the BoxOffice magazine in the mid-1960s. By then some studios started closing their animation division due to a rise in television, but the success of the Pink Panther cartoons may have led to other studios keeping it alive for few more years, hoping to duplicate the success.
(Ran November 21, 1966)
(above two November 29, 1965)
Alas, it wasn't to be. Paramount quit animation in 1967 and MGM shortly after (again). After Walter Lantz closed in 1972 only DePatie-Freleng remained as the producer of theatrical cartoons. By the 1970s BoxOffice pretty much stopped covering shorts and very few articles and ads appeared regarding them.
I've yet to find any advertisements for the later DFE stars like "Blue Racer" or "Dogfather" that was targeted to theaters. I do know of a flyer that advertised them, but they were through United Artists' television arm (I'll put it up later).