Objectives We aimed to identify populations at a high risk for SARS-CoV-2 infection but who are less likely to present for testing, by determining which sociodemographic and household factors are associated with a lower propensity to be tested and, if tested, with a higher risk of a positive test result. Design and setting Internet-based participatory surveillance data from the general population of the Netherlands. Participants Weekly survey data collected over a 5-month period (17 November 2020 to 18 April 2021) from a total of 12 026 participants who had contributed at least 2 weekly surveys was analysed. Methods Multivariable analyses using generalised estimating equations for binomial outcomes were conducted to estimate the adjusted ORs of testing and of test positivity associated with participant and household characteristics. Results Male sex (adjusted OR for testing (OR t ): 0.92; adjusted OR for positivity (OR p ): 1.30, age groups<20 (OR t : 0.89; OR p : 1.27), 50–64 years (OR t : 0.94; OR p : 1.06) and 65+ years (OR t : 0.78; OR p : 1.24), diabetics (OR t : 0.97; OR p : 1.06) and sales/administrative employees (OR t : 0.93; OR p : 1.90) were distinguished as lower test propensity/higher test positivity factors. Conclusions The factors identified using this approach can help identify potential target groups for improving communication and encouraging testing among those with symptoms, and thus increase the effectiveness of testing, which is essential for the response to the COVID-19 pandemic and for public health strategies in the longer term.