It sounds like you are using a target that will not contain any URLs, with targets such as twitter.text all URLs and mentions are stripped out and stored in their own targets. This is documented here.
So you can either search the raw text for a url by doing something like:
interaction.raw\_content substr " [www.example.com/blog](http://www.example.com/blog)"
Or you can search the links directly by doing something like:
links.domain in "example.com"
Hope that helps!