I had the same problem a few years ago. I was the quiet kid with two friends and I felt so sad and alone all the time. I later learned that if you want people to notice you're there, you have to give them a reason to. Try being more outgoing and make everyone your friend. Then people will start talking about how nice you are and you will be the good kind of popular. DO NOT try to wear flashy clothes or get people's attention by turning "goth" or "emo". People will think you're weird and no one will want to be around you. I've also learned that the hard way. Try joining sports teams or even the band. Teams like that are like one big family. They all love, support, and stand up for one another. And we all know that the jocks are the popular ones anyway. I wish you luck :)
To get noticed when you are invisible, you should start dressing to stand out rather than fit in. Try and socialize more with people you meet, schoolmates or co-workers so that they get to know you better and you get to know them. You can get more advice at http://www.peopleskillsdecoded.com/are-you-invisible/.