Coolant reservoir problem

My daughter has an Aveo 5 LT. She recently had a coolant line blow, and we replaced it. She was still leaking coolant, and it appeared to come from the plastic reservoir tank that sits at the back of the engine compartment.
My husband thought the tank may have had a leak, so we replaced it with a new tank this last weekend. However, today my daughter noticed the reservoir is empty again, and there is more evidence of a small leak.
We have no idea where the leak could be coming from. It is isolated to the area under the reservoir platform, and it doesn't look like it is coming from either of the hoses that run from the tank area to the firewall.
She is getting frustrated, and bankrupt from buying coolant, and we are at a loss. Has anyone else had this kind of leak, or have any idea what it could be from?
Thanks!

What model year?

It's a 2010

Get a pressure tester from local auto parts. Most have Loan a tool program to look for a leak..

Is it boiling out?

No, it's not boiling out as far as we can tell. We can just see some coolant below where the overflow reservoir is seated, and her car isn't overheating or anything.

I would check the hoses for the reservoir for a pinhole leak.

did you replace the pressure cap when you replaced the tank. if the evidence is under the tank or near it, it is possible the cap isn't holding its pressure and its over flowing when the car gets up to temp, and then when it cools and the level goes back down it is therefore low.