The Projects/Workspaces application does not have a search feature/mechanism as you have described for searching through parts of the project information (whether it's the feed or otherwise). Other than being on the feed page of the project and running a browser CTRL + F command to search for text on screen, there really isn't a way to do this kind of search in the tool.
I apologize if this causes any inconvenience. You could always submit this as an enhancement if you feel the feature would add value to the system. To do so, go to our Client Portal home page and select the "Request a feature" button.
If you have any further questions or if there is anything else I can be of assistance with on this pleas let me know.