Currently I am using the following code to attempt to force my ped to get into the closest vehicle when they are on foot:

            foreach(Vehicle v in World.GetAllVehicles());

                if (myPed.IsOnFoot)
                {
                    myPed.Tasks.EnterVehicle(v, -1);
                }

So far the ped reenters the starting vehicle, immediately get out of the starting vehicle and then runs away, never again attempting to steal other vehicles.

What I want the ped to try and do is steal any nearby vehicle if they are on foot. Can anybody help me out here?

The code you have given is not complete enough to assess your problem.

I suggest adding a .WaitCompletion() after the task, like so:

myPed.Tasks.EnterVehicle(v, 10000, -1).WaitForCompletion(); 

This will wait till the task finishes and times it out after 10secs.