Messi had the chance to secure all three points from the penalty spot in the second period, but the Barcelona forward saw his spot kick saved by Iceland goalkeeper Hannes Thor Halldorsson as the points were shared in a 1-1 draw.
Aguero has said that the South American nation must support Messi, who had 11 shots without finding the back of the net in the Group D clash.
"Leo is normal, he is human," Aguero told TyC Sports. "Today we have to be with him, we know that at any moment he can define a match. The first match is always difficult. Argentina want to win against everyone. I hope that the Croatia game can be better."
Argentina will look to put three points on the board when they face Croatia on Thursday night.