Plasm Network V1 is a testnet. Currently we are looking for around 50 validators all over the world!! This is a testnet like Ethereum Rinkeby, Kovan, and Ropsten. So, PLM (Plasm Network native token called PLUM) doesn’t have any values. Therefore, there is no incentive to be a validator on the testnet. To solve this problem, we will provide you with a right to be the first validator during the PoA term (between Lockdrop1 and Lockdrop2. Around 2 months) on the mainnet if you are a legit and good validator on the testnet. The Plasm team will send you a DM in the following weeks.
You can find more info from
https://medium.com/staked-technologies/plasm-testnet-launch-90d7e58328b3