Celebrating the Valentine Day is not permissible as per my knowledge because:
Firstly: it is an innovated holiday that has no basis in the Sharee`ah.
Secondly: it calls to love and passion.
Thirdly: it calls to keeping one's heart busy with nonsense matters which contradict the guidance of the righteous predecessors, may Allah be pleased with them.
So it is not permissible that anything from the signs of that holiday takes place on that day, whether it relates to eating, drinking, clothing, giving gifts, or other than that.
It is incumbent upon the Muslim to be proud of his religion and that he does not blindly follow every crier.
The Prophet (Peace be upon Him) has advised us that if we love somebody we should let them know (of course we know the forbidden relationships are not included in this advise). He (Peace be upon Him) said it generally and did not ask us to do it 'on such and such a day'. Prophet (Peace be upon Him) didn't ask us to do it only once a year but as often as we can. So are we going to obey him (Peace be upon Him) or Mr. Valentine?
[Surah An-Nisa' Ch:4 V:59]
"O you who have believed, obey Allah and obey the Messenger and those in authority among you. And if you disagree over anything, refer it to Allah and the Messenger, if you should believe in Allah and the Last Day. That is the best [way] and best in result."
(A Muslim can’t deny the Hadith of The Prophet (s.a.w). He has been instructed to do so by Allah (s.w.t) Himself. If we don’t agree with Hadith then we are not Muslims since a Muslim testifies that ‘There is no god but Allah And Muhammad (s.a.w) is His Messenger’ by believing in Qur’an but not the Hadith of the Prophet (s.a.w) we only ‘Testify that there is no god but Allah’ whereas we don’t testify that Muhammed (s.a.w) is His messenger. A Muslim needs to follow the teachings of Allah’s Messenger as commanded.)
(Translation of Sahih Bukhari, Dress, Volume 7, Book 72, Number 780)"
"Ibn Umar said, The Prophet said, 'Do the opposite of what the pagans do. Keep the beards and cut the moustaches short.' Whenever Ibn 'Umar performed the Hajj or 'Umra, he used to hold his beard with his hand and cut whatever moustaches. Ibn Umar used to cut his moustache so short that the whiteness of his skin (above the upper lip) was visible, and he used to cut (the hair) between his moustaches and his beard.
(Translation of Sahih Bukhari, Virtues and Merits of the Prophet (pbuh) and his Companions, Volume 4, Book 56, Number 668)"
Narrated Abu Huraira:
"Allah's Apostle said, 'The Jews and the Christians do not dye (their grey hair), so you shall do the opposite of what they do (i.e. dye your grey hair and beards).'
[Saheeh Hadeeth: Related by Ahmad (no. 1945), from ’Uqbah Ibn ’Aamir (radiyallaahu ’anhu). It was authenticated by al-Albaanee in Saheehul-Jaami’ (no. 8192)]
The Prophet (sallallaahu ’alayhi wa sallam) also said,
“The day of al-Fitr, and the day of an-Nahr (sacrifice), and the days of Tashreeq (the three days after an-Nahr) are FOUR days of ’EiD (festivity); and they are days of eating and drinking.”
So from the above authentic Hadith, we come to know that Prophet Muhammad (s.a.w) clearly instructed us to not follow what the non-believers do and to create our own identity which is MUSLIM which is why he instructed us to keep beards as well. Other than that Prophet Muhammed (s.a.w) said in various different hadith that Muslims have only 2 celebrations and that is their EID , there is no valentines day, mothers day, fathers day etc etc. Every day should be a mothers day or a fathers day because Islam tells us the importance of Mother and Father which we can never estimate.
An Important Point to look upon:
A Muslim is not allowed to even meet a girl alone so how can we even think of celebrating The so called Valentines day?
and still if many of you think that it's right to celebrate and these references from Sahih Hadith and Qur'an are not enough then you guys should read the ayat i'm posting below from Qur'an which says:
[Surah Al-‘A’raf Ch:7 V:179]
“They have hearts with which they do not understand, they have eyes with which they do not see, and they have ears with which they do not hear.”
Hope that's helpful.
And Allah (s.w.t) knows best.