British Transport Police say the railway lines in Blaenau Ffestiniog are being used "like a park".
Patrols are being increased in the area, and those caught trespassing will face on-the-spot fines or arrest.
A 15-year-old girl and a 35-year-old man are currently being dealt with for anti-social behaviour in the area.
"Groups have been hanging about at the station and, worryingly, on the railway tracks, where they're consuming alcohol and drugs, and having barbecues," said Sgt Gemma Jones.
"They have so far shown a complete disregard for the residents who live nearby, as well as for their own safety. Quite simply, this has to stop."
Police say they will crackdown on anti-social behaviour at a railway station in Gwynedd - including drug and alcohol abuse and barbecues next to tracks.