Met someone on holiday but only got pictures how do I find him if I have no name?

You don't. You move on with your life and ask the name of the next person you meet that you fancy.

Hard to find people you have encountered if no further information was exchanged. The best idea is return to where you encountered them and see if they are known.

You met in person? How do you meet someone you might be interested in and not know a name? This seems like a good learning experience for the next time.