Moyes brought in 'Schillo' as a free agent having worked with the 34-year-old extensively at former team Everton.
Although Pienaar, who has struggled with injury, has only played once in his side's last eight games, Moyes rates him highly along with fellow recruit Victor Anichebe.
“To be fair, looking at the transfers we’ve made, you could argue that Steven Pienaar and Victor Anichebe have done as well as anybody," Moyes told the Sunderland Echo.
“So we have to try and find another couple like that if we can.
“Obviously, I hope the players we get in can make a big difference, but more than likely the ones we are trying to get will be added to the squad to help us with numbers.
“I think that’s fundamental. Players want you to be towards the right end of the table before they choose."
Pienaar has featured in 14 games for the bottom-placed Black Cats this season.