In Deuteronomy 22:28 - 29 it says, "If a man finds a girl who is a virgin, who is not engaged, and seizes her and lies with her and they are discovered, then the man who lay with her shall give to the girl's father fifty shekels of silver, and she shall become his wife because he has violated her; he cannot divorce her all his days." This shows that forced premarital sex, or rape is also stealing, but unlike the book of exodus, this trespass provides a punishment, as the male rapist not only stole from the woman herself but from the woman's father as well.
Another example of premarital sex in the Old Testament is given in Deuteronomy 21:10. This is a case in which a man takes a woman captive and then if he wants to make her his wife he must follow the conditions it sets forth, and then have intercourse with her. Then, if she is found to be desirable he has the option of marrying her or sending her away. This passage not only possibly condones premarital sex, but maybe even divorce as well.