Tracing relatives in Northern Ireland - which website to use?

[AirForce5]

Hello,
I am trying to find a couple of relatives who were born, and possibly still live in Belfast. Unfortunately nothing is coming up on any of the family tree websites, even though I have their exact names and birthdates. It seems it is more centered on people who were born in England and Wales.
I am quite new to family tree searching, but I would love to know of any good websites where I can search for people in Northern Ireland.

It is not just for me, I am also helping another relative who would love to get in touch with a sibling. I would be very grateful if anyone could suggest a relevant website. Thanyou

Because of Irish independence in the 1920's does one search under UK records or Irish records. What year is the cut off?

Bump

This is a bit of an old thread but in case it's helpful- I think prior to 1922 it was all Ireland. If your ancestors were born in Ulster the info is probably held in Belfast, but I remember reading the archives suffered a fire and a lot is missing. I discovered ancestors born in Ireland (but living in Scotland in the 19th C), as they had a Scottish surname I suspect they were protestant and lived in Ulster
Couldn t find any websites to help me. That's not to say there are none but I was at Kew and my recollection is I was told the best way to find out more would be to good to the record office in Belfast. I gave up at that point!

Proni is a good place to start
www.proni.gov.uk

4 year old post but I live in Belfast and if I can be of any help? I think these days if you have full name and dob then Facebook is a better start shockingly.