Am I supposed to say Hi to these people?

Hi folks ,Im 20 and am a very timid person , not the awkward kind of timid but I just take a while to get used to people in general but once I do I am very cheerful and genuine. However . the thing is that its only recently that I have begun to break free from my shell and start to talk to people , be it in school or in general. In high school I used to be very self conscious about my appearance , the way I spoke , the way I "thought" people perceived me etc and so I missed out on a lot of things most kids in High school did ie parties etc . Flash forward to present day , I have matured quite a bit , I have gained some confidence and have become healthy ( used to be 210 pounds and am now 160 lbs , quite an accomplishment in my opinion) . So here is my main question , off late I have been running into a lot of my former high school peers but they never acknowledge my presence , they sorta look past me as though they don't know me . I really want to say hi to them but seeing them causes all my insecurities to come back to me . My main logic is that since they didn't really speak to me High school for 5 years , then why would they do so now . These people have added me on facebook but when it comes to face to face contact they don't care to communicate. So is it my duty to say hello ? Sometimes I feel like Im being the bad guy by not initiating a conversation or smiling at them but its just that I fear that they might look at me as the loser I was in High school . So what do you guys think I should do ? Say hi or should I just carry on with life and ignore these people ? By the way these people are not friends , they are just former class mates. Thanks for your help :)