AO World shares dropped on Thursday after the kitchen appliances retailer despite a seemingly strong first-quarter update with like-for-like sales up 30% as analysts cited concerns about the company launch in Germany later this year. Retail Analyst Nick Bubb said that the expansion into German is a "potentially ill-advised move", causing the shares to fall 4.5% by this afternoon. This means that the stock has now fallen nearly 42% since it listed on the stock market in February.Elsewhere in the retail sector, SuperGroup also dropped, while Pets at Home, and Debenhams were making decent gains.Tullett Prebon pleased investors after it appointed John Phizackerley as Chief Executive of the inter-dealer money broker. Phizackerley, former Chief Executive of Europe, the Middle East and Africa (EMEA) at Nomura International, will join the company on September 1st, replacing Terry Smith who steps down a day earlier.Mining group Kazakhmys dropped today after Canaccord Genuity downgraded the stock from 'hold' to 'sell'. saying that the recent strong rise in the shares means that the risk/reward balance has "moved against investors".Other miners such as Polymetal, Hochschild, Evrax and Ferrexpo were also lower.FTSE 250 - RisersPets at Home Group (PETS) 184.10p +4.96%Big Yellow Group (BYG) 524.00p +4.80%Tullett Prebon (TLPR) 261.00p +4.40%Dignity (DTY) 1,399.00p +2.12%Domino's Pizza Group (DOM) 543.00p +1.97%Genus (GNS) 1,095.00p +1.96%De La Rue (DLAR) 775.50p +1.91%Debenhams (DEB) 65.00p +1.88%Imagination Technologies Group (IMG) 206.40p +1.88%Bodycote (BOY) 683.00p +1.86%FTSE 250 - FallersAO World (AO.) 233.00p -4.47%Supergroup (SGP) 1,076.00p -3.84%Kazakhmys (KAZ) 308.30p -3.60%Polymetal International (POLY) 541.00p -3.05%Hochschild Mining (HOC) 158.00p -2.65%Evraz (EVR) 99.90p -2.63%Northgate (NTG) 498.00p -2.45%Foxtons Group (FOXT) 270.00p -2.17%Ferrexpo (FXPO) 140.20p -1.96%Oxford Instruments (OXIG) 1,221.00p -1.93%BC