As we execute during the second half of this year, we intend to capitalize on growing levels of tenant activity while remaining mindful of the positive inflection in supply-demand dynamics. As we look ahead, we're focused on two primary data points related to the future growth potential of our portfolio. One, the magnitude of our signed but not yet commenced pool, and two, the size and quality of our forward leasing pipeline. As a result, average commencements from this pool will have a disproportionately positive impact on NOI as they occur, providing important visibility on future bottom-line growth.
In addition, over the last quarter, we've seen a material expansion in the size of the forward leasing pipeline. Many tenants continue to prioritize move-in-ready spaces and buildings or sponsors that can provide a seamless path to growth as the needs of their businesses rapidly evolve. As a result, rent growth has returned to the market, with average effective rents increasing approximately 15% year-over-year. Looking forward, active tenant demand has now surpassed 10 million square feet, a level not seen since 2019, which was one of the strongest leasing execution years in San Francisco's recent history.
Encouragingly, the composition of demand is broad-based, supported by both traditional occupiers and the continued expansion of the AI ecosystem, which represents approximately a third of the active tenant demand pipeline in the market. Now we're seeing tangible interest migrate across our multi-tenant assets in the South of Market or SoMa sub-market, which saw a sequential increase in tour activity during the second quarter of nearly 65%. Our team has done an excellent job of driving consistent activity and capturing more than our fair share of leasing demand. In Los Angeles, we are cautiously optimistic as green shoots appear to be emerging with ongoing broad-based demand in Beverly Hills.