IIRC from the old one, you have to be close enough, be pressing forward, and then hit the attack button
I found when fighting shredder in his machine, that you could get really good at it by shoulder charging guys, and after colliding you would be in the exact position to perform a throw. with this technique you can throw enemy after enemy after enemy.
Of course, none of this may apply since I haven't played the new version yet.
--- It's not whether you win or lose, it's whether the other guy loses.
Reading this reminds me of the SNES version, in which there was a bossfight at the front of the screen shooting at the turtles. The only way to beat him was to throw foot soldiers at the screen and hit him.