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The campaign, run on the Snapchat messaging platform, ended on Sunday, when viewers watched a man wearing a clown's masked reveal the lucky number that won the holder a games console.
Prosecutors say this is not the first time drug dealers in Grenoble have used online marketing to develop their business.
They have used it to recruit look-outs and to sell packets of drugs.
"These commercial practices can certainly be considered amusing, but the effect is to trivialise the dealing," said Grenoble's chief prosecutor Eric Vaillant.