Last night, in Zul' Aman, I finally got Mojo!!! Actually, I got him twice while using up the 10 Hex Sticks I got so we would have Amani Charms for our Lynx boss attempt.
I didn't keep track of how many Hex Sticks it took overall to get the little toad, but I'm going to estimate around 30. Also, it was interesting that all the sticks I used on the side of the pond facing the entrance never netted a frog. However, when I used the 10 from last night, I was on the other side of the pond...over the bridge, of sorts. I got him on the sixth and eighth stick...so, I don't know if that side of the pond is luckier or not, but if you've been trying and haven't yet gotten him, go over the water!
It also might have to do with the fact that I've used the most sticks on that instance run. Perhaps you have to 'free' X many people before you get the frog pet. Or, perhaps it's random and I'm trying to apply too much method to the madness. ;p
Also, everywhere I have read states that the frog comes from a vendor that you 'free'. This is incorrect. When you use the Hex Stick on the frog, it turns into a larger, blue frog that hops to you and jumps into your pack. It's all automatic; no looting charm boxes or talking to vendors and hoping you see him in the window.
Good luck on getting your Mojo!