If you start HYIP or investing in them you will see you will need to exchange currencies. Because all of the HYIP will not receive same e-currency. So you will need to exchange e-currencies. Its really risky to exchange currency with people. Because if you send money at first and the exchanger does not send money to you then you have nothing to do.So you should always exchange money with trusted people, forum admins and trusted companies. If it become very urgent to exchange money with an unknown people then at first exchange low amount so that if the guy is scammer of fraud then it will not create a great problem for you.Here i have listed few companies and forums where you can exchange money.

e-currency Exchangers :

Autocambist ( Fully automatic and quick process to exchange e-currency )
Cambist
LondonGoldExchange
me-gold
IceGold

Money Exchanger Forums :

MoneyFanclub
ExchangeMoneyForum
MoneyExchangerForum
TalkGold
GoldAge

Best of luck. Have a safe exchange.