Inclusion Criteria:  Are 12-17 years old at the time of screening Weigh at least 20 kg (approx. 44 lbs) Have the diagnosis of PNH, confirmed by high-sensitivity flow cytometry (granulocyteor monocyte clone >10%)  EITHER:  Not being treated with an approved complement inhibitor (eculizumab or ravulizumab) prior to start of pegcetacoplan dosing, AND have hemolytic anemia. Hemolytic anemia is defined as hemoglobin (Hb) less than the lower limit of normal (Hb < LLN) and LDH >1.5 times the upper limit of normal (ULN); OR Currently receiving treatment with an approved complement inhibitor (eculizumab or ravulizumab) AND have evidence of ongoing anemia. Ongoing anemia is defined as Hb < LLN and ARC > ULN Have a platelet count >75,000/mm3 and an absolute neutrophil count >1000/mm3  Exclusion Criteria:  Are an adult, 18 years of age or older, with PNH Known or suspected hereditary fructose intolerance (HFI) History of hereditary complement deficiency, bone marrow transplant, or meningococcal disease (meningitis, bacteremia or septicemia) Females who are pregnant or breastfeeding