If you have a porch it can get under, look in the nooks and crannies under there. I suggest putting up posters and handing out little leaflets on peoples porches. Contact animal shelters and vets offices.
Iguanas are typically very territorial animals. He may/she not have gotten far at all.
As far as temps go.. They can go into suspended animation so all hope is not lost. Its common in Florida - Florida is not their natural habitat humans introduced them to the wild there.. The weather is perfect there for them until a cold snap comes through - They drop from trees etc when it gets too cold and their bodies functions at at a minimal. They can go through this for short periods but if its too long or simply too cold the brain will freeze then its all over.