[Alegun]

Можно так

Код:

const
 s: string = '":{"lvl":"100","progress":50483,"complete":150000},"gold":"10","silver":"187318","stop"';

procedure TForm1.Button1Click(Sender: TObject);
var
 tmp: string;
begin
 tmp:= Copy(s, Pos('"silver":"', s)+10, Length(s));
 Label1.Caption:= Copy(tmp, 0, Pos('",', tmp)-1);
end;