The Hunger Games definitely has moments where Suzanne Collins draws out the theme of loyalty through the interactions of her characters. Chapter Twelve addresses the question of loyalty during the first night of the Games when Katniss overhears the Careers talking about Peeta while she hides in the tree:
"'Let him tag along. What's the harm? And he's handy with that knife.'
Is he? That's news. What a lot of interesting things I'm learning about my friend Peeta today.
'Besides, he's our best chance of finding her.'
It takes me a moment to register that the 'her' they're referring to is me" (162).
In this moment, Katniss feels the sharp betrayal of Peeta's disloyalty to her and their friendship. The Careers' conversation calls everything she thought she knew about Peeta into question.
The Careers also ponder how Katniss got her high score, wondering if Peeta knows. Katniss wonders why he has not told them yet, hoping that Peeta is still loyal to her "that since he hasn't spoken much about me, we can stil get some mileage" out of their alleged romance (165). This scene in the chapter forces the reader to examine the price of loyalty in the Hunger Games. Is friendship enough to maintain and keep someone faithful, even through life and death circumstances?
Ultimately, Peeta will prove his loyalty in later chapters, but in chapter twelve, Collins uses the circumstances of the Games to challenge the reader's, and of course, Katniss' perceptions of loyalty.