Convenience stores at Southport and Worongary were held-up at knifepoint, with an offender fleeing the first store empty-handed, but getting away with cash and cigarettes at the second.

Police said a white Mercedes coupe allegedly used in both robberties was found on Thursday morning.

Meanwhile, a man armed with a tyre iron held up a service station in Palm Beach just before 3am.

He demanded cash and cigarettes from the attendant, then fled in a black Honda sedan south along the Gold Coast Highway.

Investigations are continuing.