Online forums are becoming a popular way of finding useful information on the web. Search over forums for existing discussion threads so far is limited to keyword-based search due to the minimal effort required on part of the users. However, it is often not possible to capture all the relevant context in a complex query using a small number of keywords. Example-based search that retrieves similar discussion threads given one exemplary thread is an alternate approach that can help the user provide richer context and vastly improve forum search results. In this paper, we address the problem of finding similar threads to a given thread. Towards this, we propose a novel methodology to estimate similarity between discussion threads. Our method exploits the thread structure to decompose threads in to set of weighted overlapping components. It then estimates pairwise thread similarities by quantifying how well the information in the threads are mutually contained within each other using lexical similarities between their underlying components. We compare our proposed methods on real datasets against state-of-the-art thread retrieval mechanisms wherein we illustrate that our techniques outperform others by large margins on popular retrieval evaluation measures such as NDCG, MAP, Precision@k and MRR. In particular, consistent improvements of up to 10% are observed on all evaluation measures. © 2012 ACM.