What is the ruling on publishing pictures of young men and women in contests on Facebook, including pictures of women without hijab and pictures of young men in swimwear?

This action is reprehensible, contrary to Islamic law and etiquette, and involves spreading immorality and inciting discord. It entails publishing images of unveiled women and men, whereas Allah has commanded both men and women to lower their gaze, as He says: (Tell the believing men to lower their gaze) and (And tell the believing women to lower their gaze). If the page is for selecting the most beautiful, then this is an enticement to sin. Those involved must repent to Allah and close the page.