The Current Population Survey (CPS) is the source of official US labor force statistics. The wording of the CPS employment questions may not always cue respondents to include informal work in their responses, especially when providing proxy reports about other household members. In a survey experiment conducted using a sample of Amazon Mechanical Turk respondents, additional probing identified a substantial amount of informal work activity not captured by the CPS employment questions, both among those with no employment and among those categorized as employed based on answers to the CPS questions. Among respondents providing a proxy report for another household member, the share identifying additional work was systematically greater among those receiving a detailed probe that offered examples of types of informal work than among those receiving a simpler global probe. Similar differences between the effects of the detailed and the global probe were observed when respondents answered for themselves only among those who had already reported multiple jobs. The findings suggest that additional probing could improve estimates of employment and multiple job holding in the CPS and other household surveys, but that the nature of the probe is likely to be important.