If you do not know where the NCP is, then you are going to have to prove to the court that you did your best to attempt to find him. Some ways of tracking down an absent parent are:
AnyWho: Internet Directory Assistance; Yellow Pages, White Pages, Toll-Free Numbers, Maps and Directions
calling 411
getting in touch with old mutual friends
getting in touch with the NCP's family
Try using the Post Office's 'Fowarded Address Requested' service if you have an old address of the NCP
If you cannot locate the NCP then you will have to publish a notice in the paper (either in the state that the child resides, or the last known place of residence of the NCP depending on the state law) The ad will run for just over thirty days, giving the NCP time to see and if desired respond to the notice (which states the intent to terminate the NCP's rights and a stepaprent adoption to follow.) If no response is received by the court within the alloted time amount, the stepparent adoption will continue as though he is not contesting the adoption.
Stepparents more often than not do need to be married for at least a year before a stepparent adoption can occur. Very few states have the limit set at six months.
Stepparent Adoption Blog