Networked Virtual Environments (NVEs) are virtual spaces where users interact by exchanging messages via network connections. Each NVE user often pays attention to only a limited visibility circle called area of interest (AOI) where interactions occur. The dissemination of messages to other users in the AOI (i.e., the AOI neighbors) thus is a fundamental NVE operation referred to as AOI-cast. Existing studies on NVE scalability have focused on system scalability, or the ability for the system to handle a growing number of total users, via multicast or peer-to-peer (P2P) architectures. However, another overlooked, yet important form of scalability relates to handling a growing number of users within the AOI (or AOI scalability). In this paper, we propose two AOI-cast schemes, called VoroCast and FiboCast, to improve the AOI scalability of P2P-based NVEs. VoroCast constructs a spanning tree across all AOI neighbors based on Voronoi diagrams; FiboCast dynamically adjusts the messaging range by a Fibonacci sequence, so that AOI neighbors would receive updates at frequencies based on their hop counts from the message originator. Simulations show that the two schemes provide better AOI scalability than existing approaches.