Mr DiNapoli controls the pension funds of public workers from New York.
Mr McGuinness said that despite recent dissident murders people in the US understood there was opposition to groups derailing the peace process.
"I have to say I am very encouraged by the outcome of our discussions," he said.
"We have been through a difficult week back home and it was very important to see if people were shaken by it here.
"It is clear that they are not."
Mr McGuinness is in America with First Minister Peter Robinson who is due to visit Chicago for talks with US firms that employ people in Northern Ireland.