They lurk in the corners of handbags, down the back of sofas and in the glove compartments of cars behind the mints and the de-icer.
Nowadays they are worth so little that if we saw one on the pavement, we might not even bother to pick it up.
Yet the great lost tribe of penny pieces, if collected together, would be worth an astonishing £65m - more than a pound for every person in Britain.
According to the Royal Mint, 6.5bn of them have gone missing from circulation since they were first issued on decimalisation in 1971.
Of course, a large proportion of them reside in large bottles on pub counters, and in those amusement-arcade penny falls machines where they form huge tottering piles but never seem to fall out into the eager hands of waiting children.
A survey suggests, however, that £26m worth are lying in the gutter and elsewhere on the streets, waiting to be picked up, plus another £11m in handbags, £7.8m in cars and £5.9m under the cushions of settees.
Together the lost pennies would weigh 22,000 tons, the same as a decent- sized Royal Navy battlecruiser.
The new penny piece came into circulation on February 15, 1971, when the system of pounds, shillings and pence was phased out. It was worth 2.4 old pennies but was much smaller than the coin whose name it took.
The ½p and 2p coins also came into general circulation, though the tiny ½p was withdrawn at the end of 1984 because shopkeepers could not be bothered with it any more.
Since September 1992 pennies have been made out of copperplated steel. Rising copper prices mean the metal in 1p is now actually worth 1.65p.
According to the Royal Mint, the lost pennies account for 38% of all those issued, suggesting that Britons no longer believe in the saying: 'Look after the pennies and the pounds will look after themselves'.
The average adult is said to admit to mislaying at least five pennies a week - the equivalent of about £2.60 a year - although quite how he or she would be aware of the fact is a mystery.
The research, based on where pennies tend to be found, was commissioned by the car maker Chevrolet, whose European arm was formerly known as Daewoo.