Dar cuerda a alguien

[ROBINDESBOIS]

In English?
This is used when you make sb think one thing, He gets confident and then it´s the opposite.

[poli]

to build somebody up/to wind someone up

[Perikles]

To string sb along? (This does not mean the same thing)

[poli]

To string sb along? (This does not mean the same thing)
To string someone along is to lead them on. You're right the meaning is
different.
To egg on is a closer equivalent.