I've worked on Prop HHH and other proposals designed to reduce homelessness in California: https://seliger.com/2017/08/30/l-digs-hole-slowly-economics-..., but none of them work, or can work, without making housing easier to build.
Edit to add: before someone mentions "mental illness" and "drugs" and other contributors to homelessness, yes those are real factors: that said, the lower the cost of housing, the easier it is for someone on the margin of being housed or being homeless to stay housed. The lower the cost, the easier it is for family, SSDI, Section 8, and other income supports to keep a person housed. As the cost of housing goes up, the number of people who fall from the margins of "housed" to "homeless" goes up with it. So yes, mental illness and drug abuse are factors, but they're factors exacerbated by housing costs. They're really red herrings relative to overall housing costs.