Aliases only work in the same shell where they were defined. Not even in a subshell we get when we run a script. (But if we sourced the script then it runs in the same shell.)

$ alias tweet=echo
$ tweet hello
hello
examples/tweet.sh
#!/bin/sh
tweet "Hello"
$ ./examples/tweet.sh 
./examples/tweet.sh: 2: ./examples/tweet.sh: tweet: not found