UPDATE 1-Beiersdorf fears investor exit-sources

* Shares extend gains, up 2 pct (Adds analyst, updates shares) HAMBURG, April 15 (Reuters) - Nivea maker Beiersdorf (BEIG.DE "Beiersdorf must deliver in 2012, 2013. If we don't, our major shareholder could lose patience," one of the sources, who works...