""Could lead", but "may not be as catastrophic". Note that these two contrasting statements are actually equivalent."

This is nonsense. I explained immediately after why it is not as catastrophic...

"Someone who purchases a house may suffer financial ruin. Or she may actually make a good investment. If she does so in poor judgement, financial ruin is more likely, but still just "could lead". Someone who purchases a house in poor judgement may still make a good investment not because of her own good judgment but because of blind market luck, or because the seller is well disposed and chooses to not exploit her ignorance."

Yes, that's why I said "could lead"... That it also may 'not lead' is implicit. What is your point?

"And, for example, a pregnancy that does not lead to a good marriage is a quick and obvious way to a social and financial ruin, which may be very hard to recover from."

Yes, and this is true for any woman of any age...

"It is not just the girl herself who tells about her virginity loss, but also the boys in question, as well as outside witnesses who observe her movements and conduct and gossip about it (orally or in writing)."

This may occur in certain circumstances, but it is still not guaranteed that virginity loss will significantly affect mate value, since the situation you describe will not happen in all cases.

"However, a problem with this is, how precisely do you appraise the damage done to a girl´s market value by various weaker and stronger signs of sexual unreliability? Who would a prospective 14 year old boyfriend be more inclined to trust: a 14 year old girl who has previously had intercourse with 4 different 14 year old boys, or a 14 year old girl who has previously had intercourse with 1 40 year old man?"

It is irrelevant for sexual market value what age of male a girl fucks. Virginity loss is virginity loss.

One major criticism I have is that you seem too concerned with present social realities and perceptions/morals. These are things that are variable across time, and across cultures. A good philosophical argument/approach should be concerned with constants, to the extent that that is possible. Things should therefore be analysed through harm, theft, or fraud. That people might slut shame or spread gossip about a girl is irrelevant since these behaviours can be discouraged or encouraged by a culture. I should add that it is also possible that baseless rumours could be spread, therefore reducing the sexual market value of perfectly chaste girls. So given the extreme lack of relaibilty of rumour spreading and such, it is strange that it should even be considered in a philisophical analysis.

Another problem I wish to address is the fact that your arguments do not apply exclusively to teenage girls or, more specifically, females under an arbitrary age of consent. They apply to all unmarried females, because virginity/signals about sexual reliabilty are assets to all unmarried women. Is it that you wish to know at what age females should be trusted to make decisions vis-a-vis virginity i.e what should be the age of consent for females? That would get to the heart of the matter...In that case, I'll have to inundate you with psychological articles and such...