I wouldn't force-feed just yet. First make sure there are no issues with your husbandry
Answer the questions in this sticky so we can help troubleshoot that for you.
http://www.frogforum.net/pacman-frog...enclosure.html

You need to keep him at the appropriate temps (so around 80). It may speed up his metabolism a bit, but if you don't have the temps correct he won't start eating for you.