There is no place for festivals like Valentine's Day in Islam due to several reasons which i will be mentioning here.
First of all Valentine's Day becomes a cause of Vulgarity. Lot of boys takes this day as a chance and tries to misbehave with girls in name of Love. Any boys picks up a flower and gives it to any girl on this day without thinking. Its completely against our moral values and religion. i would also like to ask supporters of this day that how would you feel if someone misbehaves with your sister on this day?
Secondly Valentine's Day has a pagan background. Islam not gives us permission to celebrates festivals of other religions. We are allowed to celebrate only our own festivals or those festivals which not goes against Islamic guidelines.
There are also some people who tries to justify Valentine's Day by saying that we can also show our love to other relations like Mother and son, Brothers and sisters, Husband and wife on this day which is Halal. My answer to such people is that we should show our love to these relations 365 days of the year. why limit the love to just 1 day?
May Allah SWT guide us towards the path of truth and save us from wrong path.