This was discussed in Is it ever acceptable to prod a user into accepting an answer? and in the posts linked there. The comment by Jeff Atwood is worth repeating:
I would only remind users who have shown signs they are going to stick around. Reminding a drive-by user isn't useful.
A drive-by user might have posted their question on five forums, got an answer at three, of which they read one - and it wasn't yours. Chances are they'll never be seen again, at least not from the same account. So the comments just create noise for others reading the post.
Other things to consider:
- New users can't upvote until they have 15 rep points
- They will not be notified of a comment you leave on your own answer unless they also commented there. Commenting on the question will notify them (assuming they still log in to their account, which is not a safe assumption. Check their "last seen" field: often it's the time they posted the question.)