HELP?? Update

We picked up one of the boys that my boyfriend hangs out with. My boyfriend is 22, I'm 20, and the kid is 15. In a way, we mentor him and give him opportunities to travel, with his mother's permission. We picked him up 4 days ago because his other friends decided to leave him out in the cold as a joke and he doesn't have a phone to call his mother (who doesn't have a car anyway; he called us from McDonald's begging us to pick him up because it was 9pm and 17 degrees). his mother only sent us one text message that said, "tell _______ that the whole family is at my boyfriend's". ______ said, "I don't have a key to the apartment" so we said he could stay with us.

that was 4 days ago.

she isn't responding to any text messages and isn't at the apartment. he has no clean clothes and doesn't know where the boyfriend lives.

we have sent NUMEROUS text messages to the mother, but she only replied once, saying that she was running errands and would send me the address later.

Since then, she hasn't replied.

we have no kids of our own because we know we couldn't afford to have any yet and we're almost out of money already just trying to keep this kid fed. I don't know what to do. he doesn't have any other family except for the ones at the boyfriend's house (_____ doesn't even know the boyfriend's name).

THIS ISN'T EVEN MY CHILD. I love him, I don't mind taking care of him, but it isn't my responsibility. it's his mother's.

what can I do? I really need help. We can't afford to keep this up and my period is making me extra upset. Please, any advice would help...

UPDATE:

Finally we got ahold of her. She had apparently dropped and broken her phone. To the ladies who said to call her instead, she has about 20 missed calls from both my boyfriend and myself. We dropped _____ off at the boyfriend's.. let me say that she did good for herself, finding a man with that much money. That house was HUGE. Guard dogs and all. He was carrying in groceries, so we know that he'll get fed well. Thank you to everyone who showed concern!! We will definitely be watching (even though it isn't fully our business, but it kind of is our civic duty to make sure a child is well cared for) to make sure he always has food and a warm place to sleep, no matter what.. and will take the necessary steps if need be. Thank you everyone. ❤