Someone Stole my AT&T Tilt?!?

I left my tilt in my best friends car on sunday night she said she would bring it to me monday morning, she text ed my cousin & told her to tell me she would bring it after she gets off work at 8 then she said she was to tired & would bring it to me this tuesday morning she had some things to do & she said she would bring it in the afternoon she text ed me ( I was using my moms phone to text) & asked were I put the phone for sure I said in the side of the backseat behind the passenger she said okay im looking for it 5 minutes later she text ed me & said are you sure because I cant find it, I said yeah of course im sure that’s the last place I put it, she said okay im still looking this went back & forth for 30 minutes I went to my doctors appointment & told my mom that she said she cant find my phone my mom was furious my bestfriend (rochelle) & her boyfriend (ceder) went over to our friends shortys house & she texted my cousin & said ceder said his mom bought him a tilt my cousin texted her wtf are you serious roro’s(me) missing her phone shorty said ya hes texting on it rite now, ceder is one of those wanna be gangstas he steals phones,jewelery whatever & sells it thats how he makes his money so I already know how he is I was 95% sure he stole my phone my mom called him & asked if we could see the phone to make sure its not mine he said no why would you need to see my brand new phone me & my bestfriend are on whatever terms rite now she says shell buy me a new one?!
What should I do?
Can AT&T track it for me? I have insurrance on it
Im so hurt,angry && distraught
my mom & a few other friends say I shoould drop rochelle?! What do you think?
Thank you for everyone who took the time to answer your very appreciated
Thank you so much
godbless C=