Holly, 22, is said to have received dozens of frightening and threatening messages from the culprit, who has apparently also posted her private contact details online.
A source told the Daily Star: "The person was publishing her phone number and her home address online, as well as impersonating her on Snapchat.
"It's causing real emotional upset to Holly."
According to the newspaper, officers from Cleveland Police are investigating the allegations.
Holly, from Newcastle, was 18 when she first found fame in Geordie Shore in 2011. The star and her cast mates are now filming the ninth series of the MTV reality show and their faces are known the world over.
Last year, Holly and the Geordie gang took Australia by storm when the cast filmed an entire series there.
Meanwhile, in the first episode of series eight, Holly declared that she has turned over a new leaf and is being "sassy", meaning she won't sleep with any men straight away.
Geordie Shore newbie Aaron Chalmers is attempting to win her over, but Holly has remained defiant and said she will only go out with him if he buys her a unicorn, a black rose and a star.
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