My wife left 5 years ago and I haven't seen her since; is this abandonment or am I still married?

You are married until a final divorce decree has been issued.  Abandonment can be a grounds for divorce but a court would still have to rule on it.

If you don't know where your wife is, you can "serve" a divorce complaint via "notice by publication".  This is used when a respondent-spouse cannot be located by the petitioner-spouse.  Basically, the respondent is notified of the divorce proceedings by publishing such notice it in a local paper in the area of their last known whereabouts. 

Then, depending on what state you are in, they have to reply within a certain amount of time.  If they do not, you can proceed with a default divorce.  Each state has rules about how you go about filing for a default divorce, but it can be done.