First I would say that it's probably not a question of strength but more a question or method.
The best way to 'pluck' a string IMHO is to use the fingernail. Having said that the method I like is - using a single smooth movement initially contact the string with the flesh of the fingertip and continue the movement in a way that the string contacts the fingernail and kind of snaps off of it, much like a string snapping off a flat pick.
You will need to experiment with the angles, the length of the nails etc... to get it right. Eventually you will have control of the dynamics of the note and be able to play it soft or loud or...
An alternative is to try using finger picks. They take some getting used to and can feel cumbersome and noisy until you get comfortable with them. In terms of finger picks I prefer Alaska Piks though in general my preference is flesh and no picks.
As a further note, with enough playing and practice your picking finger tips can get calloused giving you even more options.
Best of luck. I hope you stick with it. Finger style and fingerpicking can be very challenging but also very rewarding.
I hope this is helpful.
