Find all strings that are not in any file in the current directory or its children

find.sh

#!/bin/bash 

FILE=find.txt
DIRECTORY=fmep
while read f; do
    echo "Searching for $f"
    line=$(find $DIRECTORY -type f -exec grep -Hn $f {} \;)
    if [ -z "${line}" ]; then 
        echo "$f NOT FOUND"
    fi
done < $FILE

find.txt

string1
string2
string3