Background: Software development teams adopt various communication tools to support coordination and team interaction during the software development process. Among many other communication channels, developers’ use instant messaging to discuss ideas, decisions and other project related issues with team members. Due to the informal nature of instant messaging, many of these discussions and decisions are lost. This situation could be even more critical in startups and other software companies that rely more heavily on instant message tools or other informal communication channels.Aims: This work investigates the effectiveness of using a semiautomatic approach for identifying, extracting, and determining a project’s lost knowledge that was discussed using unstructured communication tools such as instant message.Methodology: We employed data-mining techniques to automatically retrieve discussions from instant message logs and showed them to the project managers to identify lost knowledge from two startup companies.Results: Our results demonstrate that the data-mining technique was capable of retrieving sentences with relevant issues discussion; reaching a precision of 75% at the first 10 relevant sentences evaluated. Moreover, the qualitative analysis conducted involving project managers shows an association of retrieved sentences with the project’s lost knowledge.Conclusion: Our findings indicate that automated approaches can be used to identify such lost knowledge in software development projects. Follow-up interviews revealed the interest of PMs in adopting such automated tools in other projects.