How to make hot chocolate drink thicker?
I believe what you're looking for is Italian Hot Chocolate which is thick and smooth.  

You can thicken normal hot chocolate with arrowroot or cornstarch and you're there.  If you search for Italian hot chocolate you can find recipes such as this one which is made with:


real chocolate (bitter sweet)
Whole Milk (sometimes cream)
Cornstarch
Sugar


If you can't find good bittersweet chocolate (don't use the bakers stuff), you can buy any good dark chocolate and forgo most of the sugar to keep the balance.  Keep the heat super low and take your time melting the chocolate.

It is super easy to make, and if you start with quality chocolate (Lindt and better) it will be a crowd pleaser and then some.