Under 16's... This is my advice to you.

Have you ever really liked someone and felt them pressuring you to do things you don't really want to do?
Have you ever thought "wow I really like this guy" so you have sex with them, not because you really wanted to but because you thought  it'll make him want you, only for them to walk away afterwards and never contact you again?
I've noticed a fair few underage girls (under 16) posting on here asking if it's bad that they've had sex, or if they should lose their virginity to someone who is pressuring them.
My advice to all of you is this: you are only ever a kid once. Please don't ruin your innocence.
Of course, some of you will be in relationships and feel like you're in love, others may just really want to have sex because they feel ready. To you, I say go for it (obviously with protection always!!!) If you're ready, if you're willing and you don't feel pressured, go ahead (I would usually recommend at least waiting until you're the legal age of consent anyway, because you'll be more developed mentally and physically). 
But if you have the SLIGHTEST inkling that someone is pressuring you to have sex, or do anything sexual, or you're not 100% certain that you are ready: DON'T DO IT!
And if you only want to have sex because all of your friends have but you haven't, or you think you'll fit in and be cool: DON'T DO IT!
Please. You can only lose your virginity once, do not throw it away to someone who you're not sure really cares for you. 
I know far too many people who lost their virginity at 14 or 15 and they hated themselves for it because they weren't ready. It doesn't just impact you when you're younger, it influences every decision you make toward men in the future.
Bottom line: if you're not sure, don't do it. You are far better off to lose someone who you "really like" by saying no, as opposed to losing your virginity, your confidence and having your innocence shattered because that was all they wanted from you.
Note: there are some women who do lose their virginity at that young age and they never end up regretting it. Just be sure that you are ready for it too.
To those of you who are that age, and have had sex with a boy only for him to stop contacting you: a boy does not define who you are. A boy does not define your confidence, nor your ability to find someone who loves you. A man will love you for exactly who you are. Do not lose the love that you have for yourself.