Make sure you have a good reason for the check. It will only be accepted to counter vandalism or disruption to Wikimedia wikis. Valid reasons include needing a block of the underlying IP or IP range, disruptive sockpuppetry, vote-stacking, and similar disruption where the technical evidence from running a check would prevent or reduce further disruption.
Be specific in your reasons. Ambiguous or insufficient reasons will cause delays. Explain the disruption and why you believe the accounts are related, ideally using diff links or other evidence.
Make sure there are no local checkusers or policies.
Reason(s): Mpb eu is a known sockpuppet offender, currently blocked for harassment. Eu mpb and Mpb Sf were obvious socks (blocked already), but Simeon denkov isn't. However, it feverishly tries to vote on a deletion discussion in favour of Mpb eu, using virtually the same arguments (including personal attacks) and even making spelling mistakes consistent with those typical of Mpb eu, which makes the account highly suspect of a yet another sock. Because of the autoblocks and the blocking of a network used by Mpb eu, I suppose the edits may come from anonymous proxies (a couple with anonymous edits have already been blocked). — Luchesar • T/C 14:26, 28 August 2016 (UTC)
+ Avantir: same as for Simeon denkov. — Luchesar • T/C 14:32, 28 August 2016 (UTC)
Adding one more to this case as the above: Scalana.--The Wiki Boy (talk) 19:34, 28 August 2016 (UTC)
Reason(s): bg:User:Owain Knight, one of the most active and good editors on the Bulgarian Wikipedia, attendant to several Wiki meetups in Bulgaria, over the last couple of days stared making really strange edits, vandalizing and deleting huge peaces of text from articles. The user did not respond to any of the messages left on his talk page, which is even more unusual for him, so we are fearing that his account might have been compromised/hijacked. Because we do not have any other contacts with him, and in the last couple of months there have been one more account hijack attempt by an address, which is connected to the Mitko12 sockpuppet group, can you please check if there is any relationship between them? The Wiki Boy (talk) 18:58, 28 August 2016 (UTC)