Functions as a transporter for creatine and as well for its precursor guanidinoacetate. Transport of creatine and GAA is independent of resting membrane potential and extracellular Na(+), Cl(-), or pH. Contributes to the process of creatine biosynthesis and distribution. {ECO:0000269|PubMed:23578822, ECO:0000269|PubMed:26376857, ECO:0000269|PubMed:31784090, ECO:0000269|PubMed:32249133, ECO:0000269|PubMed:32781157}. This is the function of ENSG00000152779 (SLC16A12, solute carrier family 16 member 12).