Two Perth teenagers have been charged for allegedly using a toy gun to fake a series of armed robberies to film and post on YouTube.

Police allege the youths, aged 13 and 16, faked robberies at a fast food restaurant, a pharmacy and a supermarket in Warnbro on Thursday. In each store, one of the youths used a toy gun to make demands while the second recorded the incidents on a mobile phone, police said.

They left each store before staff could comply with any demands.

Police believe the youths planned to post the recordings on YouTube.

Inspector Paul McMurtrie said: "What is of serious concern is innocent members of the public are being subjected to a harrowing experience in order for some misguided youths to make their social networking pages more appealing."

- AAP