URL sharing has become one of the most popular activities on many online social media platforms. Shared URLs are an avenue to interesting news articles, memes, photos, as well as low-quality content like spam, promotional ads, and phishing sites. While some URL sharing is organic, other sharing is strategically organized with a common purpose (e.g., aggressively promoting a website). In this paper, we investigate the individual-based and group-based user behavior of URL sharing in social media toward uncovering these organic versus organized user groups. Concretely, we pro- pose a four-phase approach to model, identify, characterize, and classify organic and organized groups who engage in URL sharing. The key motivating insights of this approach are (i) that patterns of individual-based behavioral signals embedded in URL posting activities can uncover groups whose members engage in similar behaviors; and (ii) that group-level behavioral signals can distinguish between organic and organized user groups. Through extensive experiments, we find that levels of organized behavior vary by URL type and that the proposed approach achieves good performance -- an F-measure of 0.836 and Area Under the Curve of 0.921.