God!! 20 BTC is such a large amount... in fact it can be life changing. I have been a victim of scams a few times, but I never lost such big amounts. So it was easy for me to forget about everything and move on. But in your case, it would have been devastating. Moving on is one of the options, but if I were in your place, then I would definitely pursue the scammers.
But back then 20 BTC was not worth what it is today. I suspect very small fractions of BTC will be worth very significant amounts in the future, so that people will wonder why we threw or gave away tens of thousands of satoshis as if they were nothing.
Bitcoin was probably pricing 22-266 dollars on that time op mentioned (beginning of 2013). So he might have lost between 440-5320 dollars. Well, that is not too much depending the person, but it's a decent amount anyway. In some countries it's possible to live for more than 1 year with such amount.
Back to the question, I think what I would do depends on the scam situation. If it were an exchange I would sue them with all other users who were scammed, at least on this point regulations are very helpful.
But if scammed by other kinds of sites I think it's harder to fill an action against them, especially the pyramid schemes, that is why it's better to just not invest.