Thanks for your reply. I did try looking for an online phone book but had no luck. One of the people I am trying to trace does not appear in electoral rolls after 2013, not sure if this means that they might have passed away.
I did also try googling for deaths of the people I am trying to trace but no luck there either. Also tried to find an online Bangor forum (there is a Belfast one which people use to trace lost relations/friends etc) but couldn't find one.
Here is some background on my search for these people: My 2x great aunt Annie Josephine Chamberlain (nee Hegarty) died in 2000. I ordered her death cert and the informant is a niece of hers (her sisters daughter I believe, and therefore a first cousin of my late grandfather). It gives the niece's full name and her address at the time. I had been trying for a few years to trace this line of the family with no luck, until I found this niece on the electoral rolls. However I'm no closer to actually making contact with them without a phone number or some way to speak to them! Was hoping that by posting online someone currently in Bangor might be able to assist me. Although this is difficult as I cannot provide any names or other details as they might still be alive.
In the meantime I'll keep searching and see what I can find.