|It is not clear what you are searching for.|
I think the following would do a logical OR with all these strings. Sounds like you want a logical AND.
findstr /G:strings.txt testfile.txt > nul
The errorlevel will tell you if any of them were found. Do you want to add only the lines that are missing? If you mean you need to have all those lines in that order, then it is a quite different problem.