Allah Swt says in the Holy Quran to men "Say to the believing men that they should lower their gaze and guard their modest". Allah Swt says to women in Holy Quran "And say to the believing women that they should lower their gaze and guard their modesty; that they should not display their beauty and ornaments". According to Holy Quran and Hadiths of Rasool Allah Swt such works like valentine's day are totally Haram.
Valentine's day also encourages Non Mahram man and women to meet each other that is against Islamic guidelines. its also the copy of unislamic culture. Valentine's day also increase vulgarity. The above points are enough to prove that Valentine's day is Unislamic and Haram. May Allah Swt show us right way.