The Mount Ousley teen was diagnosed with an acute form of leukaemia in 2007 and has spent the past five years in and out of hospital, receiving 120 blood transfusions in that time.

"I'm so thankful that 120 people I've never met before donated their time for someone they are never going to meet," she said.

"They are the reason I'm here."

Recently declared cancer-free but unable to give blood herself, the bright and happy 18-year-old has become a passionate advocate for the Australian Red Cross Blood Service.

"A lot of strangers out there were giving me blood and now that I'm healthy I want to try and give back and show the people who want to donate, or might be thinking about it, a pretty good reason why they should," she said.

She said blood transfusions had helped her fight her cancer and remain positive during her treatment.

"Chemotherapy makes you really sick, so there is only so much they can give you before you need to give the body a rest and one of the things to revitalise your body and make you feel a lot happier and healthier is the blood you receive," she said.

She said donating blood over the holidays was especially important for chemotherapy patients who rely on a plentiful supply of platelets, which only live for five days.

"I almost missed out on going home at Christmas the first year [I was diagnosed] because not enough blood was getting donated," Sarah said.

Wollongong Blood Donor Centre spokesman Chris Barwick said 7500 blood donations were needed Australia-wide to avoid a potential shortage of blood and platelets over New Year.

He said Wollongong still had 40 New Year's Eve appointments available and the Mobile Blood Service stationed at Dapto's Ribbonwood Centre still had more than 30 vacant spots.

To donate, contact the Australian Red Cross Blood Service on 131495 or visit donateblood.com .au to book an appointment.