OsmAnd used to integrate nominatim (a free online geocoder) and it just worked (but it was nearly impossible to figure out how to use the online search instead of the broken local search). Unfortunately, that disappeared a few updates back.
Organic Maps has a search function that works for addresses (and it is FOSS).
Pure Maps has search function that works for addresses (and it is FOSS).
Organic Maps has a search function that works for addresses (and it is FOSS).
Pure Maps has search function that works for addresses (and it is FOSS).