Pre-Seed Investment

I'm co-founding a UK-based business and we're looking to raise £400k in pre-seed funding. We're currently part of an accelerator, and one of the founders is based overseas but will return to the UK by mid-June, while the other is based locally. At the moment, we're focused on building our app and need a minimum of £15,000 by February to help support this process. I'm curious if anyone has advice on raising funds, as I've found that finding angel investors through LinkedIn or online can be challenging. Any tips would be greatly appreciated!