Note that I said "sexually active" and not "being virgin [sic]", because frankly, virginity is just an abstract concept. Not everyone defines virginity in the same way; it's not something quantifiable or measurable. Yes, technically, virginity is "the state of never having had sexual intercourse", but then we get into weird definitions of what sexual intercourse actually is. Is it limited to penetrating a vagina with a penis? And in that case, are all gold-star gays* virgins? And what about the hymen?
Let's start with inanimate objects. As far as I'm concerned, you can't lose your virginity to something inanimate, but not everyone feels that way. I've heard more than one person declare that they lost their virginity to an extra thick tampon. Of course, the idea here is breaking the hymen.
Many people believe that the hymen represents virginity, and that once it breaks, you're no longer a virgin. In many cultures, a woman is often not considered a suitable bride without an intact hymen, and some companies even sell "fake hymens", so a bride can bleed on her wedding night. The thing is, hymens don't need to "break". If they did, they'd have to break before a girl's first period, or no blood could come out. Hymens have holes in them already, they're mostly just a membrane around the edges. Hymens stretch, and more elastic hymens may go back to their original state, even after sex. Disease, medical examination, exercise, masturbation, and injury can all affect the hymen, and sometimes yes, there is blood. "Popping your cherry" is not always a result of sex, and certainly not a definitive measurement of virginity.
A friend once told me that virginity was lost once someone risked an STI. By her definition, she lost her virginity by having oral sex with her girlfriend, no penetration necessary. Another girl explained to me that even though she had anal sex, she still considered herself a virgin, because she was saving her hymen. Yet another admitted that she had had sex, but because her partner only lasted two thrusts, it didn't count. Everyone uses their own definitions, which is why personally, I think it's safer to use "sexually active". At any point, a person can choose to be sexually active, or not. Each time a person has sex, they make that choice again, and it's just as important.
I hate the idea that virginity fundamentally changes a person. The idea of a tainted girl is a dangerous one. Abstinence only education programs often compare a sexually active girl to a half eaten meal, or a chewed up piece of gum, or even a dirty peppermint patty. Once a girl has sex, she no longer has value. What kind of lesson is that? It teaches us that after a girl loses her virginity, the decision to have sex or not no longer carries the weight it did for the first time.
A girl has value before and after becoming sexually active, because value doesn't come from virginity. Virginity is not something you have to get rid of or protect. You are not losing any part of yourself. Most importantly, it's your decision how, when, and what you do, each time you do it.
* Gold-star gay is a gay person who's never had sex with someone of the opposite gender. Cartoonist Bill Roundy wrote an interesting web comic you can find here about how sex with transgendered men made people question his status as a gold star gay.