You answered your own question.
Yes, the card needs voltages other than 12. Some risers, generally the higher quality ones, regulate the voltage down from a single 12v source. These have a 6-Pin Molex Mini-Fit Jr (PCI-E) connector. Others utilize a mix of 12 and 5v and use a 4-Pin connector. The 4-Pin styles typically consume more energy than the 6-Pin ones - even without a card connected.
Example of what I'm using:
http://www.ebay.com/itm/131962699972Do not use the included SATA-to-6pin. You will burn up the SATA connector. Extract the pins and reuse the plastic 6-Pin if you build your own cable.