Westhouse Securities has downgraded its rating for magazine publisher Euromoney Institutional Investor from 'neutral' to 'sell', saying that the stock's valuation is looking stretched.The broker explained that the share price has increased by 12% since it last updated its forecasts and increased its target price to 1,110p in the aftermath of last month's full-year results. This takes the year-to-date rise to over 50%.Analyst Roddy Davidson said that this reflected the "solid underlying progress" the company has made with annual revenues, profits and dividends ahead of expectations, while net debt fell to its lowest since 1997."So, all in all, an encouraging rather than spectacular update which prompted a marginal uplift in consensus (we left our forecasts unchanged) and when coupled with relatively modest medium-term growth prospects [...] did not suggest scope for a significant re-rating," he said."Against this backdrop we believe the group's current valuation [...] looks stretched relative to the growth prospects highlighted above and in the absence of imminent trading led upgrades."Davidson said that growth prospects could rise if Euromoney embarks on acquisitions, especially given its new $160m long-term debt facility."However, under current circumstances our peer group comparison/ target price of 1110p suggests its stock is trading 14% above fair value. On this basis, we believe better upside potential is available elsewhere in the sector (our preferred plays are currently WPP, BSkyB, UBM and Moneysupermarket.com)."Euromoney was trading down 1.28% at 1,308p by 11:13 on Friday.BC