Is it permissible to create an account for a person who has not yet passed away, such as a Twitter account, for the purpose of ongoing charity (sadaqah jariyah)?

It is permissible for a person to create an online account and dedicate its reward to another living person. This falls under the category of gifting the reward or sharing in it. The reward will be commensurate with the benefit of the account and people's utilization of it for beneficial knowledge or righteous conduct.