I agree with what Joe Strazzere said but I also want to add that, generally speaking, it is not a great idea to compare your salary with that of others you are currently working with. There are all kinds of reasons why someone else may be making more money than you, some of which you are not going to want to hear (for instance, it's entirely possible that one of these people simply interviewed better, or else they increased their standard job offer in order to lure them away from a competitor).
This isn't to say you should just take whatever your employer gives you. If you are informed about how much money people are making in your line of work and know that people with your level of experience are making more than you are, then this is a pretty valid thing to raise. If they're unresponsive, then this is information you can use as well - they may be telling you they don't value you enough to keep you at a competitive rate.
The other point here to note is that small differences in really in my experience don't amount to much in a paycheck and can sometimes even be a little bit of an albatross when an HR department is told that layoffs need to be made or what have you. And this may be a bit on the Pollyanna side but it's also my experience that sometimes it's very valuable to take on a slightly lower salary to get your foot in the door, prove your worth, and then see the amount rise as your employers take notice.