The mortgage fintech said raising cash through platform Seedrs would help bring new deals to market sooner.
The campaign is not yet live on the crowdfunding site but interested investors can sign-up for priority access.
The funding target has not been disclosed.
Proportunity said it has helped finance more than £40m worth of property purchases this year, which translates to a 152 per cent increase on the same period last year.
In the pre-launch information, investors are invited to make home ownership “fair and accessible for all” and told that “home ownership should be a right, not a privilege”.
Proportunity is one of a number of firms now offering loans to boost the deposit of aspiring homebuyers, helping to increase both their affordability and access to larger mortgages.
In return for loans, the provider takes an equity stake in the property.
Proportunity has been contacted for comment.
