Dear friend, external masturbation might cause hymen tear although probability is much less than internal masturbation. But let me explain you a fact- tearing of hymen can even be caused even by cycling, exercising etc. So if someone is having non intact hymen that does not mean that her masturbation habit has caused it or she had had sexual activity. So why get anxious! In a truly committed relationship this little thing hardly matters. There are many good guys in this world who will think of yourself first than to just ponder upon the hymen. So please look the brightest side of life and relationship. Now a days even Hymenoplasty (a type of plastic surgery) can be done to moke over the torn hymen for over concerned ladies. But as a friend and doctor I would suggest you to stay positive and don t think of these matters much. Have a healthy lifestyle.Good luck.