While I'm sure there is a distribution-native package of memcached for your release available: You need to inform the dynamic linker of the location of shared libraries.
To do so drop your libevent into one of the paths configured in /etc/ld.so.conf (Prefer /usr/local/lib!) while making sure that you don't overwrite an existing version. If you did that, run
ldconfig, and verify your library is known to the runtime linker by running
ldconfig -p | grep libevent. After that, drop your memcached into /usr/local/bin/ and try running it again.
If that fails, do a
ldd /usr/local/bin/memcached and update your question with the results.