you do understand mass is not equal to weight correct? and that only the mass making contact with strings matters? Most cheap guitar picks are made from celluloid (at least my pick was) which is denser at for 1.3 (10^3 kg/m^3) compared to 1.06 (10^3 kg/m^3) for the human body and since Density equals mass / volume and the volume for both is the same a guitar pick has more mass.
Playing Loud
I think what might getting overlooked a bit (but others have discussed it above) is the effect of rigidity of a pick. Until you get to a pretty thick pick, a thicker pick can (everything else being equal) generally be louder if played with that intent. I think all can agree on that.
Ben and a few others have mentioned stiffening the grip on the pick. That causes a greater deflection of the string before it releases off the pick. A greater deflection in turn causes greater vibrating movement of the string. A thicker pick also allows for greater deflection before the string releases. Take a Fender thin pick and firm up your grip all you want, it will flex and let the string release much before a thicker pick (such as a BC).
Just my two cents. All that really matters to me is that a thicker pick can generally be made to play louder than a thinner one (and yes, it has different tone and feel).
mike I agree with what you said. All I was trying say is all else being equal a heavier pick which will have more mass, will make more volume than a less heavy pick.
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Thanks everyone 
This conversation really took-off all of a sudden and all the responses are really interesting to read. I can get something out of every response.
I appreciate all y’all 
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