Firstly, wearing a promise ring and being a whore aren't mutually exclusive.
Secondly, it's a very personal decision to take. I do think that society is oversexualised at the moment, and there is too much pressure forcing teenagers (even underaged teenagers) to rush into sex, but if someone feels that they are ready, and is using proper precautions, I don't see why they should wait for marriage, especially considering that so many marriages now end in divorce.