Discount for like

We haven't tested any such plugin, so we cannot recommend you the best plugin for this. But there are some plugin one is : https://wordpress.org/plugins/woo-social-share-discount-coupon/ You can try using this plugin, there are also some plugins which are paid, so you can look for paid plugins on codecanyon and try them. If the plugin is working fine with woocommerce then it will also work fine with the wplms theme.

As I mentioned above, if the plugin works fine with woocommerce then it will work fine with wplms also. Wplms depends on third party plugins such as woocommerce for pricing purpose, so you need to check if the plugin is compatible with woocommerce then it will work fine with wplms. And we haven't tested any such plugin so we cannot recommend you any plugin, you need to search for it.   Also you can use coupons, woocommerce gives you option to create coupons which users can use while checkout to get the discount. For creating coupons just go to wp-admin->woocommerce->coupons, and create your own coupons and share them with users via any means like email or anything and they can use it for discount purpose. This feature is already present in the woocommerce.