One word for "stealing something on its way to the recipient"
Solution 1:
You could use intercept.
From ODO:
obstruct (someone or something) so as to prevent them from continuing to a destination:
intelligence agencies intercepted a series of telephone calls
I intercepted Edward on his way to work
Solution 2:
Besides already-mentioned intercept, consider waylay (in sense “To accost or intercept unexpectedly”) and hijack (“To forcibly stop and seize control of some vehicle in order to rob it or to reach a destination”), and also the verb to pirate.
Solution 3:
You might consider purloin, which involves a breach of trust. Otherwise, there is no exact equivalent for what you want.
Businesses usually call losses during the transport of goods pilferage.
Solution 4:
I was thinking of to snag
but that is perhaps not a proper word?