Full-Stack Growth Builder at Joinfleek.com

Job Title

Full-Stack Growth Builder, Retention & Lifecycle

Company Description

Joinfleek.com – Series B fashion-tech marketplace backed by a16z and Y Combinator

Job Description

Join a high-velocity team reinventing the secondhand supply chain. As a Full-Stack Growth Builder, you will architect AI-driven CRM systems and lifecycle strategies from the ground up. You’ll own the entire retention engine, building dynamic tools and experimentation frameworks that move beyond static journeys to drive measurable, causal growth for thousands of global resellers.

Location

London, UK

Why this role is remarkable

• Direct impact on sustainability by fixing the broken global supply chain for secondhand fashion, already saving 9 million items from landfills
• Work at a hyper-growth Series B startup that has raised ~$50M from premier investors including Andreessen Horowitz (a16z) and Y Combinator
• High-autonomy “super IC” role reporting to a VP of Growth (ex-Deliveroo) with the freedom to treat AI as your default development toolkit

What you will do

• Architect and deploy adaptive, AI-powered CRM systems that determine optimal messaging, timing, and channels using real-time user signals
• Build end-to-end technical tooling for resellers, such as cross-listing features, to increase platform stickiness and long-term retention
• Design rigorous experimentation frameworks using causal inference and holdouts to quantify the true incremental impact of every growth initiative

The ideal candidate

• A deeply technical builder who uses AI-native tools like Cursor or Claude Code to ship production-quality full-stack systems at high velocity
• Strong analytical fluency in SQL and experience navigating large, messy datasets to derive actionable insights and experimental results
• Proven background in growth or product engineering with a focus on building automated decisioning systems rather than just managing marketing campaigns

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