The PSNI is yet to identify the sender of a "highly worrying" video shared to the PSNI Foyle Facebook page.
In a post to its page, PSNI Foyle said the "serious message" should have been reported urgently via 999.
They added that they had "no way" to reply to the person, and had only picked up the message seven hours after it was sent.
PSNI Foyle said: "Our Facebook is not monitored 24/7. It is mainly used by front line officers and we don't always have access to the system to check it.
"Quite a serious message was sent to us seven hours ago, a message that should have been passed on via 999 and we have only just seen it. There were no reports made to police and now we have no way to contact the person back.
"The message was of a snapchat video containing highly worrying content. If you're reading this now, phone us!"
A PSNI spokesman said police were working to identify the sender.
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