Unable to withdraw

The main reason is that I cannot withdraw funds is said that it is a joint account. I cannot apply for the withdrawal of funds without confirmation from other party. I need to pay a deposit of 50% to withdraw the funds.Now, the other party is just disappeared and cannot reach. I had already invested almost 600000 NT. Also, Miss Chen Yuxi who living in Singapore caused me a loss of NT$430,000, and she suddenly disappeared since the middle of March this year. Please help me to solve this problem as much as possible, thank you.