Amyloid aggregation is associated with neurodegenerative disease and its modulation is a focus of drug development. We developed a pipeline based on limited proteolysis-mass spectrometry (LiP-MS) to probe the mechanism of action of anti-amyloidogenic compounds. Our approach identifies putative interaction sites, can probe compound interactions with specific target conformations in complex extracts, and identifies off-targets. We analysed interactions of six anti-amyloidogenic compounds and the amyloid binder Thioflavin T with different structural forms of the Parkinson’s disease protein α-Synuclein. AC Immune compound 2 interacted with α-Synuclein in vitro, in intact neurons and in neuronal lysates, reduced neuronal α-Synuclein levels in a seeded model, and had protective effects. EGCG, Baicalein, ThT and doxycycline interacted with α-Synuclein in vitro but not substantially in mammalian cell lysates, with many additional putative targets. Our modular pipeline will enable in situ screening of compounds against any amyloid aggregates and mechanistic studies of compound action.