I've read the Bible, but I've not read much of any extra-biblical sources. Can you link me to something specific?
Even in Judaism, as far as I can tell, premarital sex isn't forbidden, it's just that marital sex is the ideal. So it would be Christians after the events of the Bible who decided that premarital sex is forbidden, and not necessarily the people quoted in the Bible. Perhaps. Like I said, I don't have your reference to look at, but that's what it seems like at first glance.
First, it’s clear that the definition includes adultery and prostitution.
The real question is premarital intercourse. I’m assuming the couple isn’t betrothed, as I think you can make a case that sex in that case was at least tolerated. Although I’ve largely made this posting independently I have reviewed “Does Porneia Mean Fornication? A Critique of Bruce Malina”, by Joseph Jensen. Novum Testamentum, Vol. 20, Fasc. 3 (Jul., 1978), pp. 161-184.
If you’re interested in seeing the case made that pre-marital intercourse is not forbidden, the classic reference is the one to which this replies, i.e. “Does Porneia Mean Fornication?”, Bruce Malina. Novum Testamentum, Vol. 14, Fasc. 1 (Jan., 1972), pp. 10-17
Those with university connections can probably access these through a library. Otherwise it looks like you can register for one-time access.
Independent of finding actual examples of word usage, consider what’s plausible. Is it really plausible that it was OK for an unmarried girl to have sex with someone? Pretty clearly not. Unmarried girls were supervised by the family for the whole purpose of preventing that. In Ex 22:16 the implication is that doing that effectively makes the girl your wife. In Deut 22:14 ff there’s a death penalty for a woman if her husband finds she wasn’t a virgin at marriage.
In post-Biblical Judaism the tendency was to apply similar standards to men as women, however the prohibition against men is certainly less clear (though Philo explicitly says that men are expected to come to marriage as virgins).
In the NT consider 1 Cor 7:9. That makes it clear that you were expected to marry if you wanted to have sex. 1 Cor 6:13 ff implies that sex makes the partners one body, which implies marriage.
It’s less clear about widows. I sometimes get the impression that they were freer than unmarried women.
The article by Malina maintains that there was no clear law against pre-marital intercourse. That appears to be true. However not everything is covered by explicit legislation. If a participant in pre-marital intercourse is killed for not being a virgin, it probably doesn’t matter to her whether there was a law against pre-marital intercourse.
(As always, I note that there's some question whether this kind of death penalty was commonly enforced. However they do indicate that something is forbidden.)