You have no requirement to invest in your local economy - and indeed, most people invest globally. So while all investment is ultimately funded by the working population, the working population is expanding massively every year if you look at the global picture. In emerging economies in particular, the demand for capital is sky high and one hour of saved income for you can buy you 100 work hours elsewhere in the world.
To simplify: if you work 7 hours a day, but save 3 hours worth of income out of those 7 hours and invest it in a company in a developing economy, you could be purchasing 300 hours of economic activity. So by saving, you have actually worked 300 hours that day (without your capital, those 300 hours would not have been done at all), while if you did not save, there is only 7 hours of economic activity.
To simplify: if you work 7 hours a day, but save 3 hours worth of income out of those 7 hours and invest it in a company in a developing economy, you could be purchasing 300 hours of economic activity. So by saving, you have actually worked 300 hours that day (without your capital, those 300 hours would not have been done at all), while if you did not save, there is only 7 hours of economic activity.