An Australian teenager who went missing from his home in Sydney more than two months ago has been discovered emaciated, exhausted and covered in leeches in bushland north of the city. Matthew Allen's family feared the worst after the 18-year-old disappeared in late November from Westleigh, near Cherrybrook, in northwest Sydney, and his mobile phone and bank accounts went untouched. Extensive searches of the area by police failed to find a trace of Allen, who suffers from an undisclosed medical condition. But two hikers found him alive in bushland less than two kilometres from his home on Saturday, covered in leeches and insect bites and having lost almost half his body weight. He was partially blind and suffering gangrene to his lower legs and feet. Police said they were amazed he had survived. "He was completely exhausted, completely dehydrated, suffered significant weight loss, somewhere up to 50 per cent. He was suffering from partial blindness and he had leeches all over him," said acting police inspector Glyn Baker. Allen told rescuers he had survived by drinking from a local creek, which was almost dry when he was found. Allen, who endured soaring temperatures of up to a record-breaking 46 degrees Celsius, was airlifted to hospital. "His family are ecstatic that he's alive and well," said Baker.