David Cameron was guided around Martyrs' Square by youth worker Abdurahman - who fought against Gaddafi - and Mervat.
Mervat and the organisation she set up, 3 Generation, tries to find information on those who went missing during the dictator's reign and the revolt.
Earlier, the Prime Minister toured a police training centre on the outskirts of Tripoli. He told police recruits it was "very good to be back".
I will never forget the scenes I saw in Tripoli and Benghazi. The British people want to stand with you and help you deliver the greater security that Libya needs.
So we have offered training and support from our police and our military. We look forward to working together in the years ahead.
Mr Cameron is due to hold talks with counterpart Ali Zeidan and President Megarief while in the country.
More top news
In its first test, the 30-kilowatt military laser burned through a trucks engine in a matter of seconds.
Islamic State militants have begun to raze ancient ruins at the site of the Assyrian city of Nimrud.
The mother of a boy excluded from taking part in World Book Day when he dressed as Christian Grey has insisted the outfit was his idea.