No, its a myth. The only thing that can speed up metabolism is exercise.
References :

It may work but it could be myth too.
References :

It is suppose to help if you drink at least 5 cups a day. I've just started to drink green tea with citrus to see if it helps. At least it will do no harm so giving it a go anyway!
References :

there is a chemical in grapefruit juice that speeds up metabolism ,i just cant spell it.
References :

'Metabolism' just means 'internal activity'. The 'marker' for it is HEAT. Chemical, electrical or physical activity uses energy, and produces heat.

Eating ANYTHING 'speeds up your metabolism', because your body needs to use energy by digesting it. There was even a fad diet (the 'T-factor' diet) based on the different 'thermogenic' effects of eating different foods. Websearch the name if you're interested in the theory.

There are many chemicals that will 'speed up your metabolism'. Alcohol is one; it is 'detoxified' by processes in your liver. If you are cold, your liver will do a lot of unnecessary 'metabolism' to produce heat and keep your blood warm. If you blood sugar is low enough, your liver will 'metabolise' to build sugars (normally, only diabetics can get low enough to trigger this effect, called 'gluco-neo-genesis').

The main site of 'metabolism' in the human body is the muscular system.There is no chemical anywhere that can speed up your metabolism as much as getting up and walking about does.
References :

green tea works for me!
References :