The teens posed together for a mirror selfie on the social media app.
In the black and white split image, Beckham, 17, and Moretz, 19, leaned their heads together while the budding model wrapped his arm around the Neighbors 2 actress.
In a second snap, Moretz is seen resting her head on Beckham's shoulder as he turns affectionately toward her.
The actress also seemed to show her love for Beckham on Instagram, posting a picture of their hands intertwined with one another.
Moretz is currently in London filming the live-action adaption of the Disney classic The Little Mermaid.
Beckham and the actress were spotted cozying up during dinner in Los Angeles with his parents David and Victoria Beckham, and siblings Cruz and Romeo earlier this month.
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A source told PEOPLE the young stars "were inseparable all night" and "had a massive PDA thing going on."
"They definitely seemed like a couple," the onlooker added.
Moretz and Beckham were first spotted together again in London this January – almost two years after they attended the Teen Choice Awards as dates. At the time Moretz praised Beckham's passion to Teen Vogue, simply saying, "I enjoy someone who is on my level with the seriousness kind of thing."