With all these doubler sites that claim to do it I don't think it keeps paying because of the last few that joined will lose out by not getting paid when they close up shop as they always seem to do when they want to run away will all the investors funds. 
That's ponzi you can't even double your bitcoin in placing investment or by doing investment some website are claiming that they can double your bitcoin in just a week no thats not true if you want to double or triple your bitcoin work for it work hard enjoy have some fun.