Financial markets once again have been seized by meme-stock mania. In mid-July, a frenzied rally erupted around a cohort of beaten-down companies, including Opendoor Technologies Inc., Kohl’s Corp.

American Eagle was in need of some buzz. It got some—from actress Sydney Sweeney, known for roles in television, motion pictures, "Saturday Night Live" sketches and, now, pants.

American Eagle is gearing up to unveil its fall campaign later this year, featuring Sydney Sweeney as the brand’s leading ...