Boyfriends Parents Took 32,000$ Of Money From Bank Account In His Name With Them As A Secondary Account Holder.

my boyfriend, (18M) has just recently in the past six months moved out and in with me. as soon as he moved out of his house, his whole account was drained. he does have evidence of this transaction.

originally, they were "keeping the money safe" by having them as the secondary account holder.

they are heavily manipulating him, and keeping the money from him. he is unsure of what to do in this situation, and he does not know if seeking legal action would be successful or worth his time. does anyone have any advice or things he should know or keep in mind before proceeding if it's worth it?