You can search by putting @Ian_Chimp in, and ticking the ‘Search this topic’ box and that should bring them up as search results.
Or you can filter them by clicking on their username in the topic and pulling up a usercard, and then clicking on the grey ‘x posts in topic’ button. (more info)
But for the My Reviews topic, some people will have a link in their usercard straight to that filter view. (I have one in mine 
)
You can also replicate this filter manually by adding a filter and username (no @) to a topic link like this:
https://lovehoneyforum.com/t/my-reviews/268237?username_filters=Ian_Chimp