Are you sure you want to give up soon?  As a rule, to declare an RP dead, the GM's post is the last one, because it means that nobody wants to respond to it.  If the GM's isn't the last post, and there are a couple of people who posted since the GM's, there's a chance that at least several people still want to stay, but don't have anything to write over.  Sure, you might have had the misfortune to have recruited some lazy quitters, but I'd recommend posting to move ahead the team to a point where we have something definite to do.  Then you'll be able to see if there's nobody left.

Oh, and prod people.  If someone's joined your RP, they've made a contract with you of assurance of their presence.  Make mentions, send PMs, whatever you need to remind people that they have an obligation.