For the German, Spanish, French, Russian and Portuguese versions of the movie, every TV/phone/computer screen was recreated in its respective language, as well as every typing sequence, keystroke by keystroke.
Since this movie takes place on a mock computer screen just like a previous film, Unfriended (2014), there is a small nod to that movie during the very first Facebook scene. The name "Laura Barns," a character from Unfriended, appears on the top right screen as a trending topic. It was shown very briefly.
Since they had a seven-week head start on shooting, director Aneesh Chaganty and producer Sev Ohanian hired the editors and together they made a rough version of the film, with Chagnaty playing all of the characters, that lasted for an hour and 40 minutes. They showed this version of the film to the crew before shooting began, in order to give everyone a feel for what they were making.
In the movie, David Kim (John Cho) works at a company called AppEnsure, Inc. AppEnsure is a real company, one that was co-founded by the director Aneesh Chaganty's father, Sri Chaganty, who is the CTO there. Aneesh's mother, Subha Chaganty, also works there as the Director of offshore operations.
During one of the earlier Facebook scenes, trending topics can be seen at the top right corner of the screen. One of the topics is simply "The Dress". This is a reference to a photo of a dress that became a viral internet sensation in February 2015 when viewers disagreed over whether the dress was coloured black and blue, or white and gold.
Early in the film, David chastises his brother, Peter, when he notices a jar of weed on Peter's counter. David is played by John Cho who is most famous for starring in Harold & Kumar Go to White Castle (2004) (and its subsequent sequels) in which he plays Harold Lee, a character who is a heavy marijuana smoker.
During the sequence in which David goes through Pam's old address book, the second name he looks up is Robert, who is later revealed to be his daughter's stalker. Among Pam's notes about the boy include his divorced mother being a detective in the SVPD and noting that he had a huge crush on Margot -- two major clues about those responsible for Margot's disappearance.
The word "catfish" can be seen during a Twitter search at one point in the film and also as the name of the mascot of the school Margot attends. This is a hint to the user "@fish_n_chips" being a catfish, which is a slang term for someone on the Internet who uses a fake photo to pretend to be someone else.
Robert, under his alias Fish_n_Chips, claims his favorite Pokemon is Kecleon. Kecleon is a Pokemon that resembles a chameleon and can camouflage itself. This alludes to the fact that Robert was attempting to conceal his identity to Margot.
Margot's last phone call could have been used in tracing her last location, because when her father calls, her phone rings but is not answered. This was never attempted by the detective because she wanted to divert the case.
When David calls Detective Vick after finding Margot's key chain at Barbosa Lake, Vick asks, "Is she at the lake?" before David mentions anything about a lake, one of the early clues that Vick was behind Margot's disappearance.
When David and Margot take the High School Day 1 picture, the Evercreek High School board reads "Home of the Catfish". That is another nod to the film's third-act plot twist, which involves Margot being cat-fished.
When David asks Vick what her reaction was when she found out her son was in fact conning neighbors out of money for a scam fundraiser, Vick admits she covered for him because she is his mother, which alludes to the twist ending.
When David first speaks to Detective Vick, he looks up her Facebook profile. Vick's Profile picture is of her and her son, Robert. Soon after, David first accesses Margot's Facebook page, and a profile named Robert Abolt is shown. That profile photo is also Detective Vick's son, showing he was Facebook friends with Margot. The same profile photo of Robert is shown towards the end of the film when Robert calls Detective Vick.