Dear Adriano:
A 'party favor' is a small gift or memento provided by the host to the guests at a party.
If 'he flies in young girls as party favors,' he provides young girls (let's hope that means young women) as companions for his friends at his parties. The implication is that these 'party favors' are available to the guests for their enjoyment (sexual and otherwise).
I hope this is helpful,
Petra




